Marvel Heroes is one of my gaming "guilty pleasures". It is extremely fun to play with the right people (I've never played it with the wrong people). It took me several games to realize that the designers at Nexus did an excellent job on this game.
Marvel Heroes is an odd game. It is highly abstracted in some areas (almost no tactical dimension), but in other areas it almost seems like a simulation (literally hundred of different superpowers for heroes and villains intersecting). It seems too detailed for a Eurogame, but too abstracted for Ameritrash. I had a hard time figuring out what my "role" was in the game, the first few times.
Then I realized my role: a "Marvel Heroes coach". You feel like the coach of a sports team. Deciding who to bench and who goes out on the field each round. Some characters are also forced to the bench because of injuries. While you don't call the tactical details (that's abstracted by dice rolls), you do get to call the major strategy for each fight.
The field of play is different each game because the "headlines" (problems that need super hero help) are generated by a card deck. The difficulty of a headline depends on which heroes are sent to investigate. Do you send a weaker character who is better at the type of activity happening or a stronger one who will have more challenge (but might overcoming said challenge easier)?
The dice for this game are brilliant. They allow for a "realistic" power spread between a hero like Electra (not too powerful) and someone like the Hulk (unbelievably strong) to be represented in the same game. I can't run the numbers for different dice combinations in my head so I just go with the different power names, and the dice results fit the names of the powers being used (if you are familiar with the comics).
The other stroke of genius is that you play the villains as well as heroes. This means that there is little downtime. However your primary focus is on the heroes, the villains can only react to hero activity. Playing villains well means managing your resources (villain cards) well. It took me a long time to realize that sometimes not playing a villain to allow for an easy hero win is sometimes better than spending all your villain cards (leaving nothing for the headlines which really need blocking).
If the feeling of playing as Charles Xavier (of X-Men fame), leading your team to glory, is appealing then this is the game for you. If you wanted more tactical feel (less abstraction of powers) then Marvel Heroscape might be the ticket (I prefer grand strategy so I've never played Marvel Heroscape).