I am a sucker for Go Nagai designs. Gaiking evokes the classic Mazinger style mecha. In fact when I first watched it, I though there was a Mazinger strapped to it's back. The Daikuu Maryuu has a face on its chest that gives it a goofy yet endearing look.
There are a lot of characters, but their handling makes the series feel too crowded. Most characters go through their growth arc and receive little attention afterward. Unfortunately, many cool characters suffer because of this - I'm looking at you, Lee.
The first half is average to bad. The second half is full of surprises, but doesn't really take off until around episode 23. Sadly, many people will drop it before they get to see the cool parts.
Animation 5/10 and 9/10
The choppiness of Toei rears its ugly head during the non-action scenes. However, the action scenes themselves were drawn by the same guy who drew the action scenes for Gurren Lagann and are pretty intense, so it gets two different ratings.