This is a solid campaign with a good story and, at least for now, a meh endgame. Each hero is incredibly well designed and fun to play if you like their respective playstyles but it takes too long to get their kits up and running. A level 50 character with good gear is infinitely more fun to play than a level 20 character at power level 30 and, unfortunately, you will most likely end the campaign before any hero gets even close to that. This means that you'll most likely be playing the least interesting iteration(gameplay-wise) of each character during the best part of the game. It's a disconnect that a New Game + and additional story content will fix but, as neither of these are currently in the game, it's an important thing to keep in mind.
To give you some perspective, I bought the digital deluxe edition and was able to start playing a couple days before the full release, played almost daily for a month straight and continued to play fairly regularly after that. I have 3 characters at max level 50(Ms Marvel, Cap, Black Widow) and Power Level 100+ but my next highest is Thor at Level 28, Power Level 35. So if I want to have fun, I play as Cap, Ms Marvel or Black Widow. If I want to grind to slowly get to a point where things are fun, I play as Thor, Hulk or Iron Man.
If you've read this far, know that I love this game. I've subtracted -1 Star for the amount of bugs currently in the game as they did effect my overall enjoyment of the campaign but this has the potential to hit 5 Stars with additional content and another pass at mission and enemy design. The core is solid but what's around it isn't there yet.