For those wondering, I just dinged lvl 20 guardian a couple days ago. And all I can say is WOW! My mangle (Adept I) that hit for 30-40 as a warrior, now hits for 80-90 (90 mostly). My ac went from somewhere around I think 400. to now, 1,100! But I guess I kinda lucked out on that (Had a master spell drop for me, bought all my shiny new armor. The shield that I got from completing the easy guardian subclass quest, is a GREAT addition with it's 200 or so ac. I had to go 1handed again, but I just purchased a cheapy shadowblade of zeal, and I'm good to go again. Anyways, you won't believe the difference in the amount of damage you can deal, and the amount of abuse that you can take. Good luck!
(The fun spells are lame though.... but I guess it's kinda a must have just because.)