I thought it was one of the best single player story driven shooters about, still is. For a change, there is actually an explanation for the bullet sponging and heath regen. If you play it like a straight FPS then its probably going to be pants. If you approach engagements like a cloaked super soldier with Hulk like strength, using the environment and your equipment to your advantage, exhilarating. Taking out a Korean checkpoint by means of ambush and running gunfight, leaving nothing but burning wreckage and collapsed huts was great.
I'd strongly suggest playing again (first one) now that maxing it is relatively achievable. Alien stuff was a let down though. Warhead was more focused but a little less free. I like both tbh