I used my level 23 custom light armor melee / stealth char and I thought this was kinda easy. The main quest is really all I've done, I haven't explored a lot of side quests -- and there are a ton of them. The main quest took me from 23 to something like 28 or 29, but I'm a little disappointed that my attack seems capped (33 with 1h sword Umbra) as does my AC (85), so I'm not gaining a lot of power.
![Sad :-(](./images/smilies/sad.gif)
The main quest probably took about 10 - 15 hours of game time tops. It was a lot of dungeon crawling and there really weren't a lot of story driven battles like in the main game. Like... I can really only think of one named antagonist that you have multiple dealings with before finally battling, and (s)he isn't introduced until halfway through.
Mostly, it was go to dungeon x and get item y.
As far as new treasure goes there's two suits of armor that you have to find molds and components to make, one light and one heavy set -- both also have new weapons. They seem to give pretty good stats and look cool. I've only found the gloves mold for the light armor so far and the torso / boots for the heavy armor.
There's also other misc. armor, robes, weapons and items around too -- it's not just limited to the two sets of armor. There's probably hundreds of new items.
You gain a few new powers and the ending is interesting as well, I'll leave it at that.
The world is probably about 1/2 the size of the main game's world, which is nothing to sneeze at. There seems to be plenty of lore and random dungeons to explore, which is nice.
All in all it's a cool little expansion and I recommend it to you if you liked oblivion, especially if your character can still use some advancement.