Great Patch!

[Meleena]

At its current rate (so a level one character starting today, post patch), if going solo, theres absolutly no way i can see you getting to 20 in a day unless your playing 12 or more hours. Especially without help. Your dreaming.

The rage forums on hp and xp levels post patch should be pretty biblical.

Youre doing it wrong I suppose, do you want to know what slow is?
Having aquired the 500 enemies slain achivement before getting the 15 level achievment.
12 hours is nothing for having gained 20 levels in the game, although I am 100% sure that you can get there faster MUCH FASTER, also try to party, or quit the game if you dont like it or you cant play it.
The game is fine.