Gameplay:
Shooting - The shooting aspect is similar to Gears in that it uses the cover system and the same perspective views, but that's it. The gunplay feels absolutely nothing like Gears of War, and if you try to play it that way it will seem off - and you will die. The enemies move around a lot more and a lot faster, and are smaller targets. Furthermore, they die faster and so do you. There is a lot more popping in and out and letting out shots in short bursts, whereas Gears is more of pop out and unload a clip. In Gears, going from seeing your character behind cover to aim mode is pretty much like zooming in; the center of your screen is still the center of your screen, and you could pretty much pre-aim before popping out of cover. Here, not so much. Overall, you're going to have to aim a lot more, and a lot faster, giving it a much more chaotic sense.
AI - At least in the demo, you are the only target, so the instant you pop out of cover, bullets are flying at you. In addition, you're a lot more vulnerable to flanking (and they do flank, provided they are physically able to - they're less likely to charge straight at you in any situation where you wouldn't be likely to charge straight at them), and you have to constantly relocate. These guys are really active, they run around a lot to try to get you. You won't be able to stay stationary, you have to move around too. The grenades flush you out. In Gears, they throw grenades in front of your cover, so it means you hide until after it blows up. Here, they throw it over. If a grenade comes your way, it's a sign to bail out. You will be running around looking for cover often, and it's frantic at times because you don't know if you're safe from all angles.
Melee - The melee is a perfect addition to the helter-skelter combat, and is much much much more satisfying that your typical one-hit melee kills in other 3rd person action games. While it is possible to screw up and ultimately die, most of the time the controls registered fairly easily. I daresay it's almost as satisfying as Heavenly Sword, minus the a lot of the depth of course.
Platforming - The platforming element works, quite simply. It is somewhat strange at first being able to climb some things and not being able to some others, but as you get further in it soon starts to get much more clear what can and can't be traversed. I figure when you get out of the jungle, there will be much less confusion as well. The bonus about the traversal is when it takes place during the gunplay. It just opens up a lot more variety to how the battles can take place.
Graphics/Presentation:
First off, almost everything about this game visually is stylized, love it or hate it. It's not photorealistic, nor does it try to be. With that out of the way...
The textures don't look anywhere near as shiny as they did in some off-screen pictures that we've seen - whether that's a good or a bad thing is up to you. It is important to note that they are all hand-painted, and not photo-captured. As a result the environments (at least the jungle) look almost exactly like the concept art paintings. The jungle part looks pretty much exactly as it does in the screens we've seen, so if the rest of the game does the same - wow. Anticipation total.
The lighting is among of the best out there. It's your prototypical HDR without bloom, as opposed to the "with bloom" version. If you've looked at most of the top-notch visual games this gen, you should know how it goes.
The water is really nice and reacts to Drake as he runs around in it. It's not the best water ever done, but it's definitely up there. If I had to nitpick at it, the splash effects/sprites are a bit weak compared to Crysis and Halo 3 (most namely when you shoot the surface), but the way it ripples in response to your character running through it is top notch. I haven't played Bioshock, so I can't comment in relation to that.
The animation is as fluid as it gets. The floaty feeling has been eliminated, and quite simply, moving a character around has never been more intriguing. There are so many little things, like if you stand on a ledge where only one of Drake's feet is over solid ground, he lifts up his leg to start balancing. He cringes when people shoot at him. He's not the smoothest dude on the block and doesn't move around with a badass swagger, and that may be what some people have a problem with. Once again, it is all stylized. But to mistake this for bad animation is beyond ignorant.
The camera is absolutely incredible. It's not your standard 3rd person camera that you rotate around you, it actually adjusts depending on where you are in the environment. And yet, you are in control of it. It transitions to aiming mode and cover mode and whatnot extremely smoothly, it's as if it's alive. And alive is quite frankly the best way to describe this game. The way Drake moves, the way the environments sway in the wind, the "smart" camera, the convincing enemy AI, and even the way they are constantly talking in a convincing manner (like in Halo 3), etc. This game is ALIVE !
BTW, the pirates aren't all Spanish. I heard one screaming in Chinese.