I own every "art of" book they printed, they're pretty but fair warning: they repeat their introduction and do not contain all the art commissioned for the set. Also, they hardly ever delve into concept art and draft imagery – the only one that actually lets you in on the behind-the-scenes creation is Kaladesh – I wish they did that for each of them.
Zendikar has an awesome geography section, it's well worth it as a first pick. But no overworld map which is fucking dumb, but in cannon they explain that the world never has the same topology for more than a week.
I also own the early ravnica & mirrodin books my fiance has the kamigawa cycle and brother's war cycle books and I'm jealous
those are neat too. They're hard as shit to come across sometimes, but used book stores in their fantasy section usually carry one or two randos.
If you want some huge cred find a way to get yourself a copy of the Planeswalker's Guide to Alara (which is the only print copy of that series) or the Art of the Rath cycle, which is the poster child of what an art book should be. Full of concept art and explanations.
The new artbooks are mostly story but are pretty to own and cheap to buy right now. The old paperbacks are hard to find, but are fun to keep an eye out for. The old artbooks are collectors items, and if you own them I'm very jealous