In Memoriam and Halkeginia Online are every bit as good as typical published fiction, if not better, and I've bought things that turned out to be significantly worse. I might add To The Stars (Puella Magica) to that list, but IIRC it was already recommended in a previous thread - I can't check at the moment, my internet connection is like unto wet string.

Uchibi Sasuke is pretty much pure crack. Amusing, but if you're asking that question you shouldn't read it.

Game Theory and Overlady are harder to judge. They're competently written, certainly, and I by no means regret spending time on them; however, my judgement is compromised by wanting to see more of the characters used. A lot of fanfiction is like that - you get attached to particular worlds, and want to expand on them. If that doesn't happen to you, there are better options in ordinary fiction. Of the two, Overlady depends more on comedy; Game Theory is straight drama.