One specific thing I liked, when comparing it to other FPS such as Doom 3 or F.E.A.R., was that you barely have to use the flashlight, which in other games gets boring after a while. Well... I guess this is because Resistance was not meant to be a frightening game, as those other two are. Another point in favor is that the game has a nice set of guns, some of which are pretty original and different to all other games I've seen in this area. And it's hard to run out of ammo, at least in the most basic (but useful) guns.
Speaking of other games, there are some levels that will remind you a lot to Call of Duty, and some others to Half Life 2. Not bad, but seems like developers of FPS are running out of ideas.
To conclude, let me say that playing with the Sixaxis controller, as opposed to a keyboard plus mouse, was extra nice. It was very difficult to get used to it, but in the end makes for a good gaming experience. I'm now willing to try Metroid Prime 3 or Red Stell on the Wii with its Wiimote, which surely are better in this regard.
Recommended game :-)