I have vague memories of it as a kid, but never really watched it. However, after falling in love with another Greg Weisman series, Spectacular Spider-Man, I watched all of it about a year ago and I now think it's easily one of the best Western Animation series ever made. It's got pretty much everything I would want in an action-adventure series for kids; great characters, complex characterization, reoccurring plots and arcs, and a refusal to talk down to its audience.
My only real complaints are the Avalon World Tour, which starts off interesting but goes on for WAAAY too long, and of course, Season 3, aka The Goliath Chronicles, where Weisman got Dan Harmon'd. End the series with the Hunter Moon 3-parter and you're golden.
Also, Frakes and Siritis are so much better as Xanatos and Demona than Riker and Troi it's not even funny.