I've put 200+ hours into KOTK so much of this post will contain comparisons to it.
- Less inventory management. Battleground's lack of crafting means I only use the inventory when switching weapons or adding attachments to them. On that note..
- Weapons attachments. It's great that just finding a SCAR doesn't mean I'm fully kitted out. There's still incentive to move around and loot so I can make the gun stronger, and it's super satisfying to make your guns progressively better (not to mention giving more variety to each match)
- Only 1 helmet and 1 armor at a time. KOTK frequently takes you out of the action in a gunfight by forcing you to reapply helmets and armor. In Battlegrounds I can focus entirely on the fight.
- Vehicles. This is probably the biggest failure of KOTK and it baffles me that they never even tried to address it. Needless to say it is near impossible to win a KOTK match without a car. On the other hand, I love that the cars in Battlegrounds are useful but also run out of gas quicker, are more fragile and discourage the "run and gun" strategy of jumping out of a car that is central to KOTK's meta.
- Strategy and tactics. I don't know what it is about Battlegrounds, but I felt a much larger emphasis on tactics like flanking and communication than I ever did in KOTK.
- Gunplay. Battleground's guns feel and sound amazing, and I love that the iron sights are more accurate than the over-the-shoulder reticle.
I'll probably think of some more, but those are just a few of the reasons that I love Battlegrounds! Feel free to post your own