Yugioh GX is an OK spin-off to Yugioh. It wasn't bad but it certainly wasn't good. It takes place in the future, at a dueling academy built by Seto Kaiba. The main character is Jaden Yuki, a boy determined to be the next King of Games and the show centers around his adventures. It's not the most original premise, but it carries it out somewhat well. Jaden has an outgoing personality, and is the stereotypical hero, though he has to be REALLY lucky, since he wins all of his duels. Even Yugi lost a couple of duels. His friends, Syrus, Bastion, Alexis, Chumley, and Chazz are all somewhat shallow, though they have plenty of character development through the show, particularly in the later episodes with darker tones. It's interesting to see how the characters are affected by the scenario in each episode. Speaking of scenarios, the plot sequence in each episode are usually decent, though the first season's first half is mostly about Professor Crowler trying to get Jaden expelled for humiliating him (?) when he beat him at the entrance exam. The character design is also pretty good. Humor is rare in the show, and actual laughs even rarer, with corny jokes that make you want to slap the dubbers.
Ultimately, Yugioh GX isn't the best spin-off, though it has some good factors. Good character design and development with nice artwork, bad jokes and a really odd plot.