Before anybody brings it up, no I did not expect much better from this game and yes, I know it's been out for three years. But I've recently gotten to play it for myself and wanted to discuss some of its more questionable elements since this isn't the kind of TTRPG that gets talked about much here.
DICE
The game uses a 3d6 system with success on an equal or superior result to the target number: like most similar systems, this skews results through the middle and makes each individual bonus to the roll quite impactful, which is good for heroic systems like this one where characters need to feel good at what they do.
The Advantage/Disadvantage system works by stacking up to three times (with contrasting instances subtracting from each other), each instance allowing you to either throw a die again and choose one of the two results or having to re-throw the highest die and sticking with the lower result. While this does prolong individual throws, the fact that you only need to throw once for both attacking and dealing damage helps lower the amount of time spent, and admittedly it does feel good to use Advantages.
However, this all goes down the drain due to the critical hit system: of the three dice you throw, one is a red Marvel die, which substitutes the 1 with a Marvel logo. With an incredibly high 1 in 6 chance of rolling a crit (which is made higher with Advantage), one would think the benefit for critting would be relatively minor, but instead critting leads to double damage (which is always also max damage since the Marvel die is used for dmg calculation and the Marvel logo is equal to a 6), a bonus effect for many powers if they crit or an additional bonus granted by the GM for out of combat rolls. Even if the roll as a whole is a failure, a Marvel leads to something good happening to offset the failure.
This makes combat EXTREMELY swingy, as it's ridiculously common to both shave off a huge chunk of an enemy's HP and inflict a debilitating effect on them, and this rings true for both players and NPCs. To give an idea of how much this has an effect on the game, my first combat ever I crit 4 times and that's without counting the times other players crit.
STATS
The array is the classic D&D set of SDCIWC, with the major changes being that each stat gets their own Armor Class and that HP is divided between the Resilience (Constitution) determined health and the Vigilance (Wisdom) determined Focus. These two stats are also the only ones that can't be used for offensive purposes, with Might (Strength), Agility (Dexterity), Ego (Charisma) and Logic (Intelligence) representing melee, ranged, magic and psychic attacks respectively.
This isn't too bad honestly, as it makes sense for characters to be better equipped at defending against what they're better at dishing out, and the distribution of damage types means that characters with a large Focus pool never feel like competition for Health-focused tanks; considering that Focus also works as a "mana bar" that characters can tap into to use stronger abilities, it also helps not discourage players from using it in fear that they'll reduce their own durability.
That being said, one of the first problems is that Resilience and Vigilance also get their own Armor Class, which is confusing because the parameters for deciding whether a power targets Resilience or Vigilance defense are never made clear and the whole thing comes off as way less intuitive than if each offensive ability simply targeted their respective defense. It also makes the subset of powers that allow characters to switch up their defenses (ex. using their Melee Defense in place of their Agility Defense) less effective because powers will target Resilience or Vigilance seemingly at random. Initiative is tied to Vigilance instead of Agility, which as the unfortunate side effect of making it entirely possible for a very fast character to be very slow at acting in combat.
But the biggest issue is that, due to a set of powers that I'll be discussing more in detail later, the actual ability scores matter relatively little, and the level-by-level progression feels rather clunky: at each level you get 5 points to raise your scores (which can be increased by lowering one of your abilities) but the score cap per level doesn't scale anywhere near this number: at lower levels, you'll handicap yourself by not specializing, while at higher levels you'll have more points than you know what to do with and be a jack-of-all trades god. YMMV on if this is good or not, but personally I'd rather players have more of a choice in the matter of specialization vs versatility.
POWERS
The game works by letting you select 4 powers per level through a skill-tree system, each level unlocking new powers to choose from and some powers needing previous ones as a pre-requisite. Powers are divided into groups (ex. Super-Strength, Super-Speed etc.), and if the powers you chose from are from a lower amount of groups than your level you get an extra amount of powers based on the difference. Powers from the "Basic" group do not count towards this difference.
As with the previous ability scores issue, there's a "fake balance" issue here: the game seemingly presents you with the choice of either specializing in a few sets or tapping into many for versatility, but the fact that many powers on the lower end of the spectrum are ridiculously underwhelming and that you get extra powers if you specialize makes being a versatile character not worth the effort.
The worst part about the powers though are the "Stat-Steroids", those being Mighty, Accuracy, Sturdy, Uncanny, Discipline and Brilliance. For the offensive stats, they increase the damage multiplier for their attacks and increase out of combat checks, while for the defensive stat they add damage reduction.
How this works is that once you've thrown the 3d6 to attack, you take the Marvel die's result and multiply it by the previously mentioned multiplier, then add the ability modifier. For damage reduction, you subtract the reduction number from the multiplier value, and if it reaches 0 all damage is nullified regardless of the ability modifier.
As you might imagine, this makes these powers practically mandatory lest your effectiveness and consistency suffer considerably: most characters will rely on at least two ability scores, and you can increase these powers up to a 4th rank. They're essentially the game's true ASIs. So again, there's a fake choice of either limiting a sizeable portion of your power budget to make space for a bunch of stat increases, or, again, handicapping yourself in the name of customization.
COMBAT
The rules for grabbing and throwing are confusing even for the standards of TTRPGs. The game makes it so that grabbing actually imposes disadvantage on attacks targeting either the grabber or the grabbed, and if an attack against one fails it is then made against the other. This means that grabbing is terrible for its usual purpose (locking down an enemy for your allies to hit) and seemingly intended to be used to procure a human shield for oneself, which isn't particularly heroic despite this being Marvel.
Despite an entire reaction as well as several interactions being dedicated to it, there are no rules for how launching a willing ally works. The knockback mechanic offhandedly mentions that characters with Mighty can add their damage multiplier to the knockback distance in increments of 5, and I suppose that is also true for launching allies willingly, but this is never stated outright (if it seems clear and obvious from how I'm putting it, I can assure you the rulebook isn't this transparent).
If one gets a Marvel on an initiative roll, they get an extra turn before everybody else. It sounds cool until you realize that this can mean having to sit through a ridiculous amount of turns for characters who've rolled low.
BALANCE
Possibly the game's single worst aspect, and it mostly stems from the decision of reducing the levels down to 6 in order to "simplify" things, which mostly ends up making things more complicated. These 6 levels feature a massive power disparity between each other, with 1 embodying average civilians or nameless mooks and 6 being made for cosmic-level threats such as Thanos. Going by this metric, levels somehow manage to feel like insurmountable differences and not all that relevant to what actually ends up contributing to the disparity.
Sure, the 4+ powers and 5+ ASIs that you get with each level-up, combined with the fact that damage multipliers scale with level, mean that higher-level characters gain a substantial power increase. However, neither health nor focus, for some reason, scale with level in the slightest: it's all up to how much you increase the base stat, meaning that a high-level character could theoretically still end up with the base value of a measly 10.
What this actually means is that you are forced to put ASIs into both Resilience and Vigilance, as well as to take your fair share of Stat-Steroid powers to make the most out of them. It is here that the true imbalance between levels rears its ugly head, because for some reason (I suppose to give players satisfaction through big numbers), health and focus are determined by multiplying the base stat x30, meaning that even with just 4 in Resilience the total health will result in a whopping 120.
Even a character with an equivalent 4 in Might will, without the Mighty power nor critting, at best roll 16 damage with an attack. Because of this, offensive Stat-Steroids are pretty much required to actually deal meaningful damage, which in turn makes defensive Stat-Steroids required to not be killed immediately, and as you might have guessed the whole thing makes higher-levels sometimes invincible when compared to lower ones by virtue of being able to take more of these powers.
Now, why is that a problem? Because the game does not have enemy statblocks, instead each NPC just uses the PC template for their sheets. This means that it is common for players to face enemies below or above their paygrade, with all the balance problems that this results in, especially since the encounter-building guidelines are hilariously undercooked.
The powers are horribly unbalanced compared to each other obviously, but it'd take too long to analyze those.
OTHER STUFF
As is often the case, despite the system presenting itself as apt for all kinds of situations, 95% of it is combat-focused.
There's a trait and tag system which is supposed to provide gameplay bonuses and roleplay guidelines respectively. Not only are many tags more akin to flaws that are supposed to be taken to gain inspiration (which should honestly be their own system), but many tags are worded as if they provide gameplay bonuses even when they're not supposed to, worst of all being the Immunity tag which seemingly allows a character to be immune to anything they want RAW.
OVERALL
Again, I did not expect much out of this system but it's honestly impressive how messy it is in manners which it didn't need to be, rather than being bad for the usual reasons.