IMHO Guiness is a great diversion from your ordinary brew.  In order to truly enjoy it you must not think of it as a "beer" because it isn't, it's far from it.  Think of it as a different type of beverage, nothing like a regular beer.  If you've broken in your beer palate on Bud, Miller and Coors then, yes, it's going to take a little getting used to.  I don't think it's the be-all-end-all of brews but it is a nice break from your normal brewed beverage.