|Irish spell or Italian basketball?|
From Hyroth's perspective, the geas has an uncertain purpose and an even more uncertain origin. Rather than just tell me what I am supposed to do (or find, in this case), Tim has been telling me that I feel compelled to go in a certain direction and complete certain activities. I really like this approach.
It is fun to play a character with a set of external motivations and compulsions. While I wouldn't want to do it all the time, it makes for an interesting and challenging approach to playing a character. Rather than rebel against it, I have tried to run with it.
One side effect of this is that the usual player character interest in treasure or other personal advantage has taken a back seat to completing an unpleasant task and ridding myself of a horrible compulsion.
Another side effect--and a fun one from my perspective--is that my character is viewed as wildly unstable and dangerous by the other player characters. Some of that predates the casting of the geas on me. We did have a nasty three way fight between player characters in the middle of Session 1 that led to my near death experience. My subsequent appearance as both living and even more unstable has given the rest of the PCs something to think about.
To me, this has the best of both worlds as I have to respond to an external compulsion yet this compulsion was something experienced by me in game. My of my characters tend to be party guys--but it is fun to play a character who could potentially be an enemy of the rest of the PCs.