I, primarily, play conquest. I love the fact that you accumulate points as you are taking the base now. It isn't all or nothing and if you die while in the process it wasn't for nothing.
I also love that they not only still give you a kill assist but if you do the majority of the damage but someone "steals" your kill you still get credited with a kill.
Overall game play is great and improved (running and jumping over things). They also seemed to have "fixed" the whole jumping around like a freaking rabbit in order to avoid being shot that was so prevalent in BF3. Some of the background graphics are worse which takes away some of the realistic feel that was so well done in previous Battlefield games. But I can live with that given the better overall game play and close up graphics and rendering.
They did a great job with the vehicles and some of the new weapons and perks.