Just finished the game and felt somewhat dissapointed. Thought this would have been an easy GOTY for me but it doesn't come close. I'd rate it at 7,5/10. I simply did not enjoy the gameplay as much as in UC1 and 2 (which i both easily rate 10/10).
My biggest gripes would be the gunplay/shoot-outs and the setpieces. I didn't enjoy the shoot-outs. The entire cover based gunplay is gone since enemies always come up to you or smoke you out with grenades (ND really wanted you to try out their new "throw back the grenade at enemy" mechanism and their "new and improved" melee). In fact, they shouldn't have bothered with implementing cover spots at all because they have no use. For some reason, aiming didn't seem as solid as in UC2 either.
Also, for some strange reason, i have the impression that ND made the multiplayer maps first and just implemented them into the single-player. Every shoot-out feels like a multi-player map.
Also, i fail to see the fun in the setpieces where you just have to run and get out as quick as possible. Spectacular? Maybe... Fun? After 2 times, i had enough of it.
There were other points aswell (pacing, too many location hopping, extremely formulaic gameplay,...) but these were the most important.
In short: UC2>=UC1>>>>UC3
If they ever do another one, i hope they stop trying to outdo UC2 and get back to the essence of Uncharted. I'll gladly trade in every on-rails setpiece for a bit of good solid old fashioned exploration/platforming and gunplay that involves a bit of strategy.