The game is a lot of fun but it's worrisome that it's more demanding on my system than Crysis, a game known for its incredible system requirements and pushing the boundaries of hardware. I have to play this game in 20-minute intervals and then give my system time to recover. It's like track and field in school all over again.
This game is good enough that I spent money on Kongregate for the first time just to buy an in-game bonus. A lot of fun with great pacing. My only negative feedback is that the upgrades can be confusing and unclear -- but not enough to have a serious impact on playability.