I haven't played Arena since the 90's, so I can't really remember much of anything distinct from the provinces... except for Skyrim. The Labyrinthian is probably the thing that I remember the most from Arena, just because I spent a ton of time in there. I remember being on the phone with a friend, both of us playing our respective games, trying to talk each other through the place. Good times.
I guess it's on the map, so I guess it will be back. Very cool. They could port it over and I wouldn't know it, but I'm hoping for something bigger and more complex... perhaps a 3rd level that was discovered after the events of Arena.
The one thing I do miss are the riddles. Where you actually have to type in the answers, no lame multiple choice. And there actually wasn't much of an internet back then, so there was no Googling for answers
Whenever I got stuck, I used to tell the riddles to anyone who would listen to get some ideas. Games were more fun back then.