Well, haven't heard of this game till now, so late to the party. The screenshots urged me to give it a shot and I'm pretty impressed. Played the game from start to finish in about 2 sittings. Graphics are really good. I experienced no noticeable lag, with "intense" graphics and max resolution. Gameplay was simple with a 2 button mouse (dunno about trackpad/magic mouse). Pretty much went through classic mode with the pistol and mostly sniper rifle, and later in the desert missions saved up coins and got the plasma rifle, which freakin owns. Have not tried the other modes yet....
Replay value seems high since there are achievements and other "mini goals" to obtain. You can even buy outfits with the coins you earn during the game.
I would say give it a shot if you never played the game.