In the game, losing reverts your monster into a human form. There isn't any "genetic editing" from the sky. In the fiction of the game, the monsters started off as human, with the wolf being an actual wolfman made huge by ingesting a food additive. In the movie, the mysterious sky object creates three distinct beasts.Another difference in the game and movie is the game makes it clear from its awesomely '80s promotional art there are three monsters. In the trailer, the reveal of the crocodile beast is basically "also, one more monster for some reason." Not that that's a bad thing.
The three creatures then presumably spend the rest of the movie smashing buildings while being attacked by police and military forces, just like in the game.
Games differ from movies in how they can be pretty satisfying even when built on the thinnest of premises, so coming up with something a little meatier for the movie makes sense. It probably wouldn't be an enjoyable experience to sit and watch a giant wolf, ape, and mutant crocodile punch downtown Chicago for 90 minutes, but the film releases on April 20, so who knows? Seth Macy is more animal than man. Follow him on Twitter @sethmacy.