This got me through so many shifts working in a call center. Could download PuTTY and run it from my user folder without admin permissions and then connect to one of the servers.
Been awhile since I played, but I remember my first ascension was Draconian Skald. I think the rules have changed quite a bit, but I used to love Troll Monk of Cheibriados, too. Stoneskin + Stoneform and a shield of reflection absolutely WRECKED the Elven Halls. For every step I'd take the elves would get like 4-5 turns and fire off a volley of arrows. I'd take practically no damage and a large portion of them would get reflected back and kill the elves themselves. Literally just waltzing through the place. Slow is life.
Transmuter used to be a lot of fun, too, but they changed it significantly over the years. I remember playing as a Felid one time and I died while in spider form. Because Felids get several lives, I reincarnated on the same level, ran back to my corpse and condensed it into a poison potion to chuck back at enemies.
I find it to be one of the simpler roguelikes to learn, but it takes awhile to master and there are some very cool interactions once you get the vibe.