Thing is, if they changed it too much, the battlefield fans wouldn't buy it.
They already changed it enough to get some moaning it isn't a proper battlefield game. There's no jets, no tanks, the vehicles are present, but by and large swapped for civilian vehicles which don't usually appear in battlefield
They've changed the game modes, with only really TDM and conquest staying the same. They messed with the TTK and the weapon balancing, and changed the class balance too.
About the only thing wrong with it is that its not got a brand new engine and uses the BF4 engine. But given how long DICE LA spent getting the BF4 engine right and sharing that with Visceral. This is a GOOD thing. The last thing we needed was for visceral to try and write a new engine and then go through all the work getting it right, when DICE LA was literally doing just that with the BF4 engine while hardline was in production.