For me Uncharted 4 was as perfect an ending as I could ever have hoped for, it was paced perfectly. If you look at the games in terms of the story it was trying to tell then a faster pace and an overload of action would have ruined that.
The slow build in the first 5-6 chapters was perfect for introducing the gameplay mechanics, characters, their past and current situations: all while allowing the player a decent amount of control. There's two prison breakouts, a boat chase in a storm, a more personal husband and wife scene, an underwater dive for lost cargo and a stealth mission at an auction in Italy. Plenty happens and is expertly written and performed in a way that made me, perhaps more than any game before it, feel like I was actually playing through a movie. I couldn't put it down.
The game has some very moving and touching moments too, and the villains are also the best the series has seen.
Combat is leagues ahead of the older uncharted games and some of the best in a third person action adventure game I've experienced.
Sure there could have been more shoot-outs, the game isn't perfect (no game ever will be) and there aren't as many wow looking set piece moments as UC2-3. But if you can look past that, and if you love the characters and a well told story with lots of varied locations, high production values, fantastic gameplay and an actual sense of pacing rather than just mindless killing from beginning to end, then this is one of the best games in the genre ever made for my money.
If you dislike narrative driven, cinematic games then you'll probably hate it though. So I can understand why some people have strong feelings against this type of game. Personally I love these games.