I haven't beaten it yet, if I had to guess I'd say I'm about halfway, probably a bit under, so my final judgement will have to wait a moment.
It's a great game for sure, and it has the usual Naughty Dog polish, and adventurous feel. It's almost flawless technically. I do have to say gameplay-wise it's kind of beginning to get stale, Uncharted isn't really fresh anymore. I've recently completed Tomb Raider, right before getting started on Uncharted, and that game felt fresher due to some new and interesting gameplay elements while Uncharted for the most part seems to still lean on what worked before. What worked before was good though, obviously, but, I'm not sure to put it, it's kind of lost it's edge. I was impressed by the car level in Madagaskar I just completed, and the PS1 Crash Bandicoot easter-egg is probably the greatest easter-egg I've ever seen, barring maybe John Romero's severed head in Doom.
Anyway I realize that it's hard for a series such as this, which inherently doesn't keep reinventing itself because it keeps featuring the same characters in the same continued story, to remain original. So it's probably best that this is the last Uncharted game (hopefully). Uncharted 2 remains the best easily, it's one of the best games ever made, and for now I'd also put Uncharted 3 above 4, but we'll see how it develops. Uncharted 4 is great, but to me it's not the 'classic' 2 and 3 were.