In trying to recreate and update some of my old levels, I've also run into more differences. The way Airship ground is rendered has changed a lot, at least in the SMB3 theme. No longer will a pillar of ground 2 blocks wide form a mast. Now it's just siding like wider ground. The underside of Airship ground is also much blockier unless you use slopes, which I guess is the idea. I mostly like that change except it means I can't put decorative portholes in some places I'd like them to go.
When a pipe comes out of a wall, there's special graphics done to make it flush with that wall, but when a pile comes out the side of another pipe, no such luck. It's bewildering to me.
I wish scroll stop were a bit easier to use. I appreciate that it can be done in any direction, but hate that only ground and hard blocks work for it. At least make slopes and pipes work too! I've been wrestling with it a bit. I also wish that I could make a vertical area one screen wide without resorting to scroll stop. I was hoping that if I left the right (or left) half of a vertical area empty, the screen wouldn't scroll into it, much the same way that a horizontal area won't scroll up if you don't put anything above one screen height. No such luck.