Warlocks can be disappointing. I had been a lock for a long time, playing fanaticly since vanilia but my passion for the class faded. Propably because the concept of the class gets tiring easily.
Priests have become very insteresting recently and tbh shadow is a realy good copy of affli if not better.
It has what locks lack in survivability and can sometimes play the role of the dotter better. Not to mention you can switch to healing if things get pinchy.
If you somehow get tired of shadow you can always go healing. By now i've played every healing class in the game and i can say that priests are by far the most interesting healers out there.
Also, look at cataclysm. The incoming abilities look awesome and tbh i cant wait for holy grip.