Comic fans and hack/slash fans unite for a good time.
I think that as a prerequisite to make it through this game you must be either a Marvel comics fan - I mean a regular reader with some knowledge - or a serious hack & slash gameplay fan. This game delivers on both. I will address the comic fan first.
There are is a good selection of Marvel heroes to play on your four-man roster from the get go including big timers like Spidey, Thor, Iron Man and the entirety of the Fantastic Four. There are also some lesser known playables like Deadpool, Moon Knight, Ms. Marvel (Warbird) and Luke Cage. Every character has 2 alternative outfits to unlock and most have 3. Each outfit grants different abilities to its wearer, so don't overlook that (especially Ghost Rider's "Original" - nice bonus power.) The characters have unique and player specific powers and fighting styles that don't feel like they repeat themselves even when you get to the unlockable characters.
And how about those unlockables? Dr. Strange, Daredevil and Black Panther are just a taste. Part of the fun in the game is meeting all of the many, many NPC's, fighting the many bosses and sub-bosses that you know from the books. Another part of the fun is all of the unlockables.
The game rewards you for your comic book knowledge, giving you boosts to your stats for assembling comic book specific teams like the Defenders or the New Avengers, or teams based on character traits, like ninjas or women (duh.) One of the cooler aspects is that eventually you can create your own team with your own logo and whichever characters you want and it too will give you a bonus power up of your choice. Personally I have not jumped into this because I haven't unlocked the Surfer yet!
The gameplay is solid and team dynamic (who does what type of damage and how) adds a nice level of strategy. the player moves are unique and appealing, Captain America's Shield attacks, for instance are particularly nice. Unlockable characters are not the same as playables, although there are types. For example Daredevil does not play the same way as Deadpool or have the same moves but he serves as a close combat specialist in the same way Deadpool does. The moves look and feel accurate.
The hacking and slashing is repetitive and does lose its appeal in weaker levels. What is weak to one, however may be strong for someone else and mostly I am basing their strength on story content and setting. I am not keen on the Asgard levels as a setting but they do offer a break from the typical dungeon crawling layout in level design.
The special mission side games are repetitive as is the gameplay but there is enough variety and the characters are different enough from eachother that switching them up and experimenting with powers is rewarding as you level up your players and try to unlock your favorite hidden gems. This is even one hack & slasher that I will likely play through again, as you can load in yourleveled up characters when you beat the game and start again with your personalized, fully powered up super-team.