I found it wholly forgettable. The animation was truly terrible, possibly worse than the original Gaiking's on the whole. Some of the characters were truly awful (and rarely on-model), the plot was bland.
Did you even make it to the first episode with Face Open? The series does have some well animated battles. Proist was a fairly memorable villain too. Beginning wasn't really good, and did nearly nothing to catch the viewers attention, but the series was also never really offensively bad either, so getting through those initial episodes isn't that hard.
I can easily name probably a dozen 00s episodic Super Robot series that are completely better in every way, and the 00s haven't been a heavy period of Super Robot production.
If you restrict yourself to episodic shows, I really don't think you can do that...
If you're Yasuhiro Imagawa, you've personally directed like 4 of the 10 or so best scenes in any mecha show ever. You get to have all the ego trips you want. Even the absolute worst thing Imagawa's directed (that would be Seven of Seven) is still a show roughly 10 times more interesting in every way than Gaiking Neo.
Maybe it's because I'm a big Mazinger fan, and I've even watched the 92 episodes of the original tv series, but I just disagree here.
Imagawa took a long time to go anywhere with the characters, and still wasted screentime on a bunch of irrelevant people who aren't even Mazinger characters or connected to Mazinger in any way besides original creator (meanwhile cutting things like the Getter crossover that was originally planned, mentioned by one of the creator's blogs when the anime started airing).
So, you ended with things like Kouji and Boss becoming friendly rivals and Sayaka falling for Kouji just due to who the characters are, rather than any on screen development. I'm not even complaining about Kouji's mother, who was an imported character, but one integrated into the plot, although I felt like her strong presence just hurt Kouji during most of the series. Anyway, I'm talking about her helpers... who just took a lot of screentime throughout, had some random death scenes, returned without almost any explanation... and basically were completely unimportant overall even after all that.
There was also just incoherent material too, like the Mazinger Z getting beaten up by the Energer, which even tanked hits initially, even though the later didn't have Super Alloy Z. Add to that the slow pacing that made weekly episodes feel too short, and the series just suffered. Most of the "twists" at the end (at least, from the good guy's side) didn't even make much sense either, like the Great Mazinger appearing for a single attack and then disappearing or the entire hidden army thing (which would have been completely unusable if the Mazinger army had mortally wounded when their units were shot down initially).
Gaiking doesn't have a good beginning, and it's fairly standard at times, but half of the series didn't feel like it was on some autopilot. Developments actually happened on screen and the power of the machines didn't randomly change.