I've been on the Test server since it started, only on the live server a couple times a week for raiding/end game stuff and hanging out with friends. The test server is tough sledding though, you're literally the first line of QA, and there are a lot of bugs and abilities that don't work. They do fix them somewhat quickly, and with so many people on there, a lot is getting reported and fixed. That said, it's tedious, not incredibly fun, and the population on Test is dwindling because it can be frustrating.
The cool part of the Test server is seeing the Mastery trees though. These things are enormous and the abilities greatly change how the class plays depending on what you select. When they work of course. There are essentially 26 classes now, 28 if they ever get the bard in. Mastery is in for all the tanks and healers. Seems like Wizard, Summoner, Enchanter are next. You just have to get to level 5, then you can open the Mastery tab in your spellbook at bring up the trees. They are way bigger than Enshrouded, closer to PoE. You have 70 nodes per side per class. For class specific abilities. In the future, you'll also get general mastery which is kind of like AA in EQ. So, PoE types of trees. Class Mastery is fixed to one point per level, General Mastery will be more open ended and you'll get those points similar to AA grinding, but also with quests and drops.
A lot of the classes are very interesting. A Shaman can be an Oracle or a Fateweaver. Fateweaver is all buffs and debuffs. Oracle is healing. You can hybrid to an extent, but it's really two distinct classes with unique abilities. A Druid can be a Perserver (heals) or a Storm Herald, and if you go SH, you lose excess to all your healing, but can really pump DPS. You get a lot of unique abilities and appearances. Mastery is very cool. It's so far above their pay grade, what they are trying to do, it's insane. We'll see if they can pull it off, a lot of the abilities aren't working yet, but when they do, it's pretty good stuff. They need to get the Mastery done for all the classes and then do the next release. A lot of people are going to like this. If they get it working.