Just a quick review, because I don't feel that most of the reviews online reflected my gameplay experience.
As usual, BF1 has strong environmental and cinematic special effects. There is a wide array of WW1 weaponry, some of which have some iconic and endearing quirks. The maps are visually interesting and attractive.
That being said...
The gunplay feels very sloppy. When you get a kill, it rarely feels deserved. When someone kills you, it often feels like it's more about the frenetic nature of the map design than someone who is literally just better at the game than you are (whether that's true is another matter, of course! ). The overuse of lazy environmental effects that limit your vision range by X distance instead of having anything to do with location or geography is abundant. Regenerating healthbars really detracted from the theme. The mustard gas is more annoying than additive to the experience (though it requiring a gas mask therefore inhibiting use of crosshairs lends it some interesting tactical use!) There is no hardcore mode. The server browser was largely empty, with only 2 servers with people playing. I don't think the game has any mod support, as usual, so if you want more content you just have to wait and pay up.
Really, it just feels like a simple BF4 with lots of WW1 gimmicks. Some of the new map modes are interesting attempts. There were clear efforts at some innovation, but it mostly resulted in shallow changes. I certainly don't think it was the iterative cash grab that some other franchises are criminally guilty of. There are very obvious signs of effort and love in a lot of respects, I just don't think it came together very well.
I read one review comparing it to Bad Company 2, which I recently booted up a few months ago and played for a few weeks, and this game is about as far from BC2 as any of the BF games have ever been, aside from Hardline (I didn't play Hardline, but the theme was pretty distant). Bad Company 2 had very crisp gunplay, levels that were just the right size and design for the player counts, with just enough insanity to keep you on your toes but not so much that it left you feeling somewhat helpless.
I actually encourage anyone who is interested to buy this game, because of Origin's solid return policy. Your experience may vary completely, and there's no reason to take my opinion too seriously while you can just experience it yourself. I just figured I'd put my thoughts out there, since I felt that a lot of the online reviews were incredibly generous in most respects. I think a lot of folks were just happy that we got a differently themed BF, so they gave it far more leeway than they should have.