If I were to rank the different series of DRAGON BALL based on worldwide consistence I say it would be 1. DRAGON BALLZ 2. DRAGON BALL and by a country mile 3. DRAGON BALL GT. Over the years DBGT has gotten a bad rap and I completely understand and to a certain point I agree with it. First some backround back in 1994 Akira Toriyama completed his series DRAGONBALL(the comic was call Dragon Ball from beginning to the end the "Z" was added to differentiate between the 1st half and the 2nd half.) the anime of it was going to end in about a year and television. So the Production company TOEI decided that Dragonball was too much of a moneymaker ot end so it started production on Dragon ball GT to continue the adventures of GOKU.
So it was a money grab. But is there anything of worth in GT?
POSITIVE: It continues the story of Dragonball Z. Popularity for Dragonball was at an all time high so giving more of what people wanted isn't necessarily a bad thing.
NEGATIVE: It continues the story of Dragonball Z. In this case giving people what they "think" they wanted was a bad thing. Since GT wasn't based on any existing material and didn't have any major involvement from Akira Toriyama the series(primarly the 1st part) suffered.
POSITIVE: Unlike the end of DBZ, DBGT had a definitive and satisfying ending. DBZ ended as a sort of passing the torch over to the new generation but a lot of fans weren't happy about what Goku did at the end.
NEGATIVE:If you look at the ending again to Dragon ball it makes sense and does fit the character of Goku. Even if he wasn't going to train to battlesome new threat, he would train someone else and pass on what he knows to the next generation(Just as Master Roshi did with him) Truth to tell I'm actually fine with either ending even though I can understand why some may like one and not the other.
POSITIVE:The production company wanted to do something different and change the tone and direction a bit and have it be more like early Dragon Ball. There was a vocal group of fans who to this day say that Dragonball was at it's peak "BG"(before Gohan).
NEGATIVE: That vocal group turned out to be the minority. When Dragon Ball began the main characters and the readers where the same age. As the character grew and matured so did the reading audience. So while they may have been nostalgic for the early Dragonball what wanted now was more of the"Z" portion. It's not a coeincidence that about a 1/3rd through the series GT became more like DBZ. Unfortunately it was too little too late at that point.
POSITIVE:Introduction to new characters.
Negative: The already established character really didn't have any purpose. Some make cameos. Others such as Vegeta (with a laughable mustache!) they do something and then don't play into the rest of the series to any real degree.
Negative: Uub does nothing. At the very end of dragon ball z it's assumed that Goku is passing the torch to Uub and the further adventure in the dragon ball universe if made would follow him. Goku and his friend's story were over(hence the "Z" in dragon ball z). So going back and and making Goku the main character again is repetitive.
POSITIVE: A great soundtrack and interesting character designs. While GT only had one opening it had 4 ending themes and each sounded completely different from the last and not something you would think sounded Dragon bally(is that a word? It is now I guess). The designs of the existing characters looked like a logical extension of the series.
NEGATIVE: The animation moving from DBZ to DBGT didn't increase significantly.
NEGATIVE:No significant involvement from Akira Toriyama. He did a couple of character designs and gave the series it’s name: Dragon Ball GT(Grand Touring)*It is interesting that the “grand touring ending after the first story line though*.
NITPICK: The black dragon balls were created by (evil)Piccolo before he merged with kami. I know this is a retcon but seems like a pretty sloppy one. Because what that means is that Piccolo(and most likely Kami) knew these things existed and did nothing about it. I label this as a nitpick because the blackstar dragon balls are the macguffin of the series and wasn't created by Toriyama.
Recommend: Yes I do recommend the series. It’s not as bad as you heard, it is fun and exciting. HOWEVER you need to know what you are in for. I wouldn’t say “GT” is a side story but think of it as more of a “Filler Series” or an alternate continuity. You can consider it a continuation or not. It’s entirely up to the view to decide.