Fans of the series will appreciate the incremental upgrades, but don't go expecting anything groundbreaking.
The "main" series of Battlefield games have always brought big, sweeping changes with them. From Battlefield 1942 to Battlefield 2 to Battlefield 3, each game felt substantially different from the title it followed. Battlefield 4 on the other hand, feels way too similar to Battlefield 3. Fans of the series will appreciate the incremental upgrades it brings to the table, but I couldn't shake this feeling that it felt more like a Battlefield 3 expansion pack than a whole new game.
EA went all out with its Tokyo Game Show demo of the game, going so far as to actually set up 36 PS4 units, so players could try out a full 16 v 16 player round. I played the new "obliteration" game mode, which is an odd mix of capture-the-flag and domination, and a round lasted about 20 minutes.
This may be because of how used to the PC controls I am, but Battlefield 4 just felt wrong on the PS4 controller. Unlike Titanfall, which felt very natural on the Xbox One controller, with BF4 i felt like I was constantly fighting it. In particular, mapping all of your weapons to the D-pad felt awkward, and having crouch and prone as the same button quickly got annoying.
It may sound like i'm heaping a lot of negativity on this game, but I actually enjoyed it quite a lot. Hardcore Battlefield fans will appreciate a lot of the "quality of life" changes introduced in BF4. Vehicles feel a lot smoother - helicopters in particular are a lot easier to control - and the map overview screen has vastly improved. In BF3, it's sometimes difficult to tell where your squadmates are when choosing to spawn on them, but in BF4 it is immediately made obvious.
Classes have been streamlined even further, and each class has a whole suite of new weapons and gadgets to play with. I particularly liked that you could customize both slots of the gadget loadout, IE: as an engineer, you can choose to have a repair torch and mines, whereas previously choosing mines would lock you out of the repair torch.
But probably the biggest change to the game comes from the actual engine. Battlefield 3 already looked pretty nice but BF4 is beautiful. I got to see "leveloution" in action by bringing down a full skyscraper in the Shanghai map we were playing on. The water effects are just gorgeous - waves sweep across the shores and the water reacts to objects that enter it.
The bottom line is, if you still play Battlefield 3 every day and are hungry for more, you're going to thoroughly enjoy BF4, but if you played BF3 rather casually and are expecting as big of an upgrade as the jump from BF2 to BF3, you won't see it here.