Marvel Heroes, the MMO by Gazillion, has been spotted at San Diego Comic Con as a playable demo at the convention.
Reviews of what has been visible in the game say the game is much more like Diablo series than an MMO like World of Warcraft. Taking control of an actual Marvel character, and working with others, a lot of what has been described is similar to the way Marvel: Ultimate Alliance 1 and 2 played out. However, it seems the game is designed to unlock characters as you play. This aspect is similar to League of Legends, or Sony's Marvel Superhero Squad browser game.
The lead designer of the game was the designer who created Diablo 2, so it is understandable the game would move in that direction. Public play areas will exist in the game, making the experience different than a standard Diablo-style game where all the maps are isolated.
Lagspike.tv is not sure how this will go over with the general public. With games such as City of Heroes, DC Universe Online, and Champions Online, the inability to create your own character will push many people away from purchasing the game. The Diablo-like aspects, however, may draw people in, as will the ability to play as your favorite Marvel hero.
The latest character to be announced in the game is the Human Torch. Massively has an article up at http://massively.joystiq.com/2012/07/12/marvel-heroes-turns-the-flame-on-with-the-human-torch/ with a short description of the character.
In addition, Marvel is running a live feed from San Diego Comic Con at http://marvel.com/sdcc2012