Here is a small list of recent changes.
You can now earn spar coins from winning spar matches. These can be spent in the coin shop to purchase unique hats and accessories. You get spar coins from defeating unique opponents (resets every 24 hours). There are some other guides that go into more depth on the system.
Capture The Flag:
CTF has been brought back along with a dedicated shop. You can join CTF matches via queue (similar to carnival events). Participating in these matches will earn you CTF coins that can be spent in the shop for unique items, hats and accessories.
The entirety of swamp town has been updated with new / updated graphics, shops locations. There is also the auction house which deserves its own section (Perception has a good guide in the FAQ Sub-Forum).
There is a new daily rewards system that you can find in the main menu. There is a reward that you can collect each day (If you have been online for at least 30 minutes). There are also VIP only rewards on certain days. Along with this are challenges that will give unique rewards. These challenges require certain amount of daily rewards to be collected to unlock the challenge. There are also some challenges that require VIP daily rewards.
So yeah, that's all the major changes I can think of. There are a bunch of smaller additions that I haven't mentioned here, but you can probably find that in the in-game news.