Dragon Age: Origins was pretty good and I thoroughly enjoyed it for a good two or three weeks but certainly doesn't come close to being the best RPG ever. Played through on a mage character who ended up having Healer and Arcane Mage (can't remember the names of the specialisations). I also played through a second Rogue character, but didn't complete the game with her.
Did you get Blood Mage from the desire demon? I chose reputation boost with Allistar since with Morrigan and Sten in my party, decisions normally pissed off Allistar, but he is a very powerful character so I felt I needed to keep relations good with him.
However, there's a glitch that I didn't realise until afterwards: with the Desire Demon you can take blood mage, save the game, go back to last save before you talked to the Desire Demon and you still have the blood mage specialisation since they carry on over saves.
Or you could just play with Morrigan (you can chose witch Mage character you want yo use) and then talk to the desire demon, your own character won't loose any relationchip points.