Normally, I'm really not into this sort of game. I like sandboxes, yes, but immense violence tends to turn me off. But this? I'm glad a friend pointed it out to me, because it's one of the best games I've come across in a long time.
Jumping around New York City like a crazed mutant squirrel on steroids never gets old. Mercer's many bladed appendages are fun to play with, and when you've had enough of that, you can destroy helicopters by throwing sofas and shopping carts at them. The side events are suitably challenging, and they'll keep you occupied for a while. And the difficulty modes. Easy mode makes you feel like the godlike character you're playing as. Hard mode is /hard/.
On the gameplay end, it's... cathartic. And over-the-top. And fun. XD But the story end is what hooked me.
People often complain about Prototype's plot, but I really don't understand why. You need to put in some effort to figure out what's going on, but once you work out events and what happened... it's beautiful. There is so much delicious, delicious irony, and it really makes you feel the creepy conspiracy bit. The cutscenes could have been longer, imo, but anything with Alex and Dana ended up either sad or hilarious. And it really says something that the man-eating viral abomination is the /hero/. Well, anti-hero. Of all the factions in the game, he's the only one that doesn't want everyone in Manhattan to die horribly.
The only beef I have with this game is (the sequel, but let's forget about that) the fact that civilians are all suicidal. Military A Is
can be hilariously stupid too, but those fallacies are just fun to point out and laugh at; it's the civvies that get annoying. It's literally impossible not to kill at least several hundred of them during the course of the game, because they will dive in front of your tanks as you drive and run in circles while you're trying to clear out a Hive.
Seriously, though, this game is worth getting.