Not sure exactly how many hours I've put in, but I'm level 18, playing "Caster Only" on my first playthrough. Having a lot of fun spamming Fireballs until things die a painful death in front of me.
Being a pure caster can be problematic however, Snow Leopards and Bears kill me in 2 hits, so most of my fights involve me healing in 1 hand and fireball throwing with the other and hoping I kill quickly.
Its super fun however, loving it.