I was thinking of going back to WoW, haven't played since Cata. Is it worth $30?

I've recently gone back and I've been enjoying myself. I'm not playing anywhere near as seriously as I used but, but I'm having fun gathering mounts and pets and stuff.

If you log into your account you MIGHT have a 1 week free trial available to you, check for that first and then you can see if you like it. Also you can try contacting support and asking if they can give you a few days trial time, sometimes they're able to work some magic for you if you haven't been active for a while.

Cata was bad, Panda was 10x worse, idk about the newest xpac though. No flying mounts are usable while lvling in the new area like the panda xpac which just killed it all for me. No flying mounts, no thanks :p

I liked the talent system updates (less choices, but more meaningful ones) from Mists. I also really liked the warlock changes. I think now your items may also change stats now based on your spec (but just the newest expansion's gear I think)?

Sadly, I personally got burnt out on the type of game WoW is, and I still didn't enjoy it when I went back. However, I do think it has changed enough for it to be worth retrying if you enjoyed it before.