4KIDS didn't dub the 4th season of GX, because they wanted to focus on dubbing 5D's instead. Hence only 3 seasons of GX are available to watch outside of Japan. They will probably dub the 4th in the future.
I've seen most of the series, GX was my favourite, although 5D's is pretty epic!
We're talking about the original version, right? If so, then I still watch it from time to time. I know that they show the English dub on Saturday mornings, but I only watch the Japanese version since it seems more complete. I've watched every episode of the Battle City arc in Japanese, and it was much more enjoyable than the dub. I've started watching the Doma arc in Japanese, and I'm also enjoying what I've seen so far. I only watch one episode per week, but I may start watching a few more in order to catch up.
I'm watching it in Japanese, and I think it's fantastic. I know that a lot of people complain about it, but I really like the story and the new characters that were introduced in it. I also like the duels that were featured, even though they weren't the most creative duels in the series. The Yugi versus Rafael duels were cool to watch, since Yugi lost the first one.
I watched the original, GX, and most of 5D's. My favorite sagas are Battle City from the original, season 1 and 2 of GX and I haven't decided what my fave from 5D's is yet. I heard a lot of people complain about the Doom arc that followed after Battle City. It had some good duels in that series but at the same time as a whole I didn't like everything about it. I think that arc also ruined Mai's character. She hates Yugi and friends for not saving her even though they did save her, and Joey nearly died dueling Yami Marik simply to save her. Mai is so ungrateful.
I liked Yami Marik too, but Yami Bakura was my favorite character. Thief King Bakura was also impressive, but I believe that he was only being used as a pawn by Yami Bakura. Something like that. I never really understood how there were so many Bakura running around in the original series. It made things really confusing at times, but I do know that the bad one died and that the good Bakura (Yugi's friend) survived.
The series has been over for years, so that shouldn't need to be put in spoiler tags IMO. And honestly, it was sort of obvious that the villain would "cease to exist" or that the villain would be defeated at the very least. The villains always get defeated by the protagonists in children's anime series :/
Yami Bakura's fate was known even before the anime finished it up, it was based on a Manga. Well everything but the Virtual World, Doom, and Kaiba Grand Prix sagas those were filler arcs. I also think Kaiba vs Joey in the Battle City was filler as well. Never understood what the point of that duel was, it just felt like it was made to give Kaiba a win after losing to Yugi.
I'm currently watching 5D's(Watching the recent dubs as they come out, currently it's the World Racing Grand Prix, kind of want to just watch the subs since I hate waiting a week for the next episode but I prefer to watch Yu-Gi-Oh in dub) as it airs on TV for me. Also watching original Yu-Gi-Oh(Battle City Semi Finals) since it's on the same day as 5D and on the same station. If only GX would air on the same day and station...or just air, I don't think I have any station to watch it.