This game is very good. I played the beta way back, and wasn't extremely impressed. It didn't feel like any of the other Red Faction games, because it isn't anything like them. But after having intensively played campaign mode in the retail version, I feel that this game is just as good as the original Red Faction. The multiplayer seems to be almost the same as the beta, except with more weapons/maps obviously. I think that the graphics are better too, but I don't have a means to directly compare the two.
Anyways, I paid $80 for two copies of this game (one for friend and one for myself), and I feel that it was money well spent. While I don't consider this game to be GOTY material, it certainly is a candidate for being the the game of the summer. Plus it can be had for ~$40, so it is worth the price of admission.