I literally just played through the game again for the third time just before Christmas. I agree that the pacing was too sombre and slow for its own good, mostly because there was too much climbing and downtime, and too few combat scenarios, but I personally love it none-the-less. In my opinion there isn't really a better historic pirate based narrative out there in any moving medium (film or gaming), and the next best thing is probably something like The Goonies.
Story and sense of adventure.
I love the way the story builds up, takes you all over the world, and also keeps delving deeper and deeper in to the mystery of Avery's treasure. What should have been a simple loot hunt, ends up turning into some massive pirate tale that is full of twists, turns, grandiose tests, puzzles, trials, tribulations, partnerships, societies, cities, betrayals, civil wars, back stabbing, murder and all the rest.
Then the way it intertwines with the characters in the game and takes you globe trotting, is awesome too. One minute you're in some Panamanian prison, the next some Mission Impossible style heist in Italy, then sliding and swinging around historic ruins in Scotland, then driving around the muddy plains of Madagascar, swimming and exploring a paridisical tropical island, making your way through a rich historic secret city, seeing a huge spooky pirate ship and so on. There's just so many cool moments, locations, areas, layers and elements to it.
Also Nate and Elena are charming, Nadine bad ass, Rafe a cool villain, Sully awesome as ever, and Sam a decent addition. The ending as well, is really beautiful.
I personally didn't really see the issues with Sam that you did, mostly because I felt Drake himself allowed himself to get caught in to the lie mostly because he himself was not content with his own life, and was secretly looking for an excuse to get back in to the game. The story of Alcazar being far fetched was sort of besides the point. It was the excuse that gave Nate a way back in.
Combat and encounter design
The other thing I really enjoyed about the game is that the actual combat gameplay itself is exceptional. The best it's ever been and some of the most fluid, dynamic and rewarding in any third person shooter out there. Whilst imo there are too few combat encounters and set pieces in the game, what there is, is generally really well done.
To go into some of the things I think makes the combat so rewading.
1).
Greater emphasis or reward factor to precision shooting and less bullet spongeyness, dependant on player skill and aiming competency. In UC4 essentially every weapon in the game can take out the vast majority of enemies with a single well timed bullet to the head (this is also true of previous Uncharted games), no matter what weapon it is. This headshot multiplier gives the combat an added skill ceiling, and greatly rewards players who are more precise and methodical with their aim and recoil management, and to reiterate, not just with certain specific weapons, but
every weapon in the game.
2).
Hit detection, hit reactions and fluidity of animations are class leading in UC4. Whilst it might not have the visual element of extreme gore, blood splatter etc, it compensates by having insanely good hit reactions and animations, that give a super accomplished sense of feedback and response to the combat, making every bullet, grenade etc super impactful.
3).
Fluidity and precision of controls in the game are also top notch. Everything just feels super polished and good to play. The contextual animations, melee, cover system, obstacle detection and movesets, responsiveness to shooting, climbing, jumping and all the rest. There's a fluidity to combat and gunplay that makes everything feel better.
4).
The weapons in the game pack a punch and sound both realistic and fantastic, especially with a good pair of headphones. This is one aspect the game really improved on from previous titles.
The following points are less specifically about gunplay and more about the combat in general.
5).
The mobility, dynamism, fluidity of combat and freedom of approach options in the game are simply put, top tier. The different mechanics, systems, tools etc in place allow for players to seamlessly and effortlessly switch between gunplay, stealth, melee etc, and constantly dynamically traverse environments mid-combat, in a quick and responsive way.
You're never going to get this sort of mobility, verticality and dynamism from most if any other third person shooter.
6).
UC4's arena / level and encounter design is some of the best in the business. Several of the combat encounters or arenas in the game are orders of magnitude more layered, dense, open-ended and broad, with considerably more approach options and verticality than most third-person shooters.
Not only are there a huge number of different levels of height, but the way they are interconnected is genius, plus you have the lasso rope swinging, swimming, ledge shimmying, climbing, jumping, grass and all sorts mixing up how you can traverse or manage the space.
Anyway, thought I'd offer a more comprehensive answer, so there you go.