As far as I know Ascent (the server they use) still doesn't have any scripted boss fights.
Maybe Karazhan, but I don't even think they've done that.
Arena is buggy when it's actually functioning, and everyone sucks. Battlegrounds work sometimes.
It's fun at first running around with ridiculous loot that you've never had before, but it gets old when every other person you see has it too.
I suppose as a whole there's just not as much to do at 70 compared to on a live realm. But I guess if you don't want to do too much then it's okay WoWScape is probably the most stable private server for how many users they have. When new patches come out it takes some time to update the servers to them, too, which means you'll be a few weeks behind the live realms. Again, though, this probably won't be an issue if you're more casual.
Oh, and there is an infinite amount of spell and talent bugs:
http://www.ascentemu.com/forums/viewtopic.php?f=11&t=486
