Prototype is definitely not a bad game, it just isn't the must have action title it could have been. As Alex Mercer, you have access to some insane abilities that seem to unleash a level of creativity and uniqueness rarely before seen in gaming and the action provided as a result is quite intense at times, but this intensity just doesn't last long enough. The mistake Prototype seems to make is assuming that just because the gamer controlled character can do all these physically impossible things, it must mean he is fun to control.
But that just isn't always the case and it certainly isn't a constant source of enjoyment from start to finish. Such a game still needs the environmental detail and atmosphere to impress, the story to immerse, the variation to fuel, none of which Prototype does nearly well enough. Give it a rent by all means, but TweakTown wouldn't recommend a blind purchase, unless you're open to "one and done" gaming purchases.