Not a whole lot, the game stopped being updated a while ago. You can check the update log on NFMM's website for the specific features you missed. Phyrexian and DivineSpirit released add-ons for the game, which add their own unique functionality to it.
The game itself isn't as active as it was in 2014, but as usual if you login, see a couple people on, and play a few matches, the room will fill up depending on the day/time.
NFM Skyline was released by West. It's quite unique so I'd check that out. -U- died and SF formed. SF is basically the new -U-. MW lost some good players with the creation of SF, and a bunch of new clans formed/dissolved.
There's more but that should get you relatively up to speed.