So I picked to be a Mage for the first time ever on the game.
I bought the game the day it came out.
So tell me whats the benifits of becoming a mage in Oblivion?

Higher tier spells! Getting your magic skills higher to unlock the more powerful spells can be fun.
My first few characters never got higher than novice in the 6 schools so I never got to play with the powerful spells.

And of course if you prefer pure role plays, it only makes sense for a mage to do the Mages Guild quests and gain access to the Uni, unlike using a character who doesn't really use magic.