It's definitely inferior to Uncharted 2 in pretty much every way, but I still had a great time playing it. I completely agree that with this third game the lack of any redesign or polish on their core shooter mechanics have really started hurting them. It still has the same floaty feel that the first one had, but without the amazing reload animation (Reload anims in the first game, still best in the business, srsly guise). For me then it actually wasn't as much the shotgun dudes that bugged me, I got some mad respect for them fairly quickly, but rather the RPG and grenade launcher dudes that always resulted in hit deaths out of no where. One of the things I liked the most about UC2 was how agile and exciting you could make firefights by constantly moving around, and with UC3 it really felt like they put a dampner on that, making it much harder to be out of cover, at least on normal difficulty.
Again, still think its a great game but sadly nowhere near UC2's awesomeness~