It's really awesome in my opinion. Some people may think it's monotonous, but fucking hell man, i (prepare for "what Bloo said earlier in another thread" refference) I LIVE FOR THIS SHIT! Well actually this is exactly what i've alwyas wanted from a game. Running up buildings, throwing people at helicopters, consuming my enemies and turning my body into several stuff, i can't get bored of this, seriously wtf! My advice though is to keep having fun with what you can do until you max everything out, then have fun some more, and only then do the main "quest" of the game, otherwise it's probably pretty short.
About Extinction now, "good rental" won't make me wanna play it, so meh, maybe when it comes to me begging.