It's pretty cool.
So first off, let's get to the "down" parts.
Less powers. Sacrificed for better powers, more useful powers. It's all good.
Less NPC's. Who needs that many? They had the necessary characters to complete the story. Isn't that all that matters?
Less equipment. This does strip down the RPG element. They get replaced with badges, which upgrades the entire team. I guess it works but... Eh...
Less Sim missions. None are character specific. None tell the background of the characters. So they are rightfully called CHALLENGES. Still wish we had better/more sim missions though.
Mission replay. Same as the first one. Just checkpoints.
Now, the extremes have been switched with fusions, which is much nicer in my opinion. Now, c'mon, ALL the extremes, no matter how cool or different they looked, just did the same thing, clear out a room. It doesn't matter if it was character specific, it just wasn't that diverse.
This time around, there are different types of fusions. Guided, clearing, targeted, you know. Each are good for different types of situations. People say there isn't much variety, but they haven't tried coming up with different fusions for each of the 24 (25 for Juggs) characters. I like the way they did it. Simple, organized, and flashy. The only complaint that I have is that if only one man is standing, you can't fuse with anyone, so unless you have two people alive, you're dead.
The gameplay is just like the first one. Which isn't necessarily a bad thing. But with the RPG focus stripped down, it feels more like a beat 'em up. But that isn't enough to stop it from being fun.
Now the "focus" of the story is the Civil War, which is a war between heroes. So much emphasis put on it. Guess what? The Civil War part is no longer than the prologue or the conclusion. So much for that being the focus of the game. Both sides are both pretty bad, although Tony's is slightly worse. More missions for that particular part would have been much appreciated.
Characters is what makes this game unique. Some fan favorites have been kicked out, letting lesser known heroes/villains become playable. Even if you don't know them, these new additions are powerful and fun to play as. With the exception of Venom. That is all.
The campaign is much shorter than the first one's. But it has two sides to pick, and even if it isn't much different, it still adds replayability. And it's funness will prompt you to come back.
Now the final boss is awful. I'm sorry. If you don't want spoilers, stop reading. The final boss is...
Nanite Nick Fury. The nanites are nanomaachines gone crazy. I know, last time we had Dr. Doom, now we have ridiculous, microscopic things.
Nanite Nick Fury was a cool idea in my opinion. Until I found out his powers were just rip-offs of other heroes and villains. How uncreative can you get? So many other games have done that. It's not cool anymore. Dr. Doom stealing Odin's powers and Apocalypse stealing mutants' powers. C'mon.
So it's all good, ignoring the disappointing final boss, a shorter campaign, a weakened Venom, and the lack of sim missions. Hopefully some DLC will add characters and missions to make this game more enjoyable. But as it is now, it's still a whole lot of fun.