It's the biggest thing from BF4 to BF1 that I don't like. Vehicle play (tanks, specifically) is not as fun, dynamic, useful, etc. in BF1 as they are in BF4. Other than that, I think BF1 is a nice upgrade in most areas compared to BF4.
It also seems like there are far fewer tanks available in this game. Maybe DICE needs to create a couple huge maps and give each team 5 tanks or something. Don't really have any maps like that so far in BF1.
EDIT: I just played a few rounds in BF4. Maps like Silk Road, Firestorm, Dragon Pass, etc. Waaaayyy bigger than anything in BF1. When will BF1 get some giant maps like that? I think it would really help with the vehicle play.