Gurren Lagaan is, in a nutshell, about exponential growth. Humans start out hiding in underground cities, tunneling with drills. The drill, a tool based on the concept of a spiral, becomes metaphorical throughout the series as the humans emerge from the ground, confront a species of "beast men" that had driven them underground, and continue to prosper at the series progresses.
The main heroes of the series exponentially gain power and ability and eventually obtain political power as humans retake the earth and even begin to dominate space.
The scale of the battles and the creations of the human species increases exponentially, playing into the spiral theme. The main enemies, once the humans learn about the world outside of the underground habitats in which they were once confined, are known as the "anti-spirals".
We see the characters mature and age as the series reaches its end. It's kind of rare that an anime follows the progress of characters over such a long amount of time. That's part of what makes it so interesting.
This is kind of a mecha anime although not in the typical sense like Gundam.
It's a mecha anime in the OTHER typical sense. Like Mazinger Z or Getter Robo. So, if you even want to make the general genre distinction, more super robots than real robots.
In fact, there are a lot of pretty clear references to Getter in the series, some probably intentional, others coincidental. I am pretty sure spiral power glowing green is probably just coincidence, because green means glowy radiation in TV. But yeah, if you like some of the themes in TTGL, you might consider checking out the Getter Robo manga. Some of it is rather silly (and dated as all hell, the series started something like in the mid-70s) but you'd see where TTGL grabbed some influence from it pretty easily at times, particularly once it starts really getting into its themes of evolution.
Gainax usually does make some fun mecha shows, though. Usually ones everyone's heard about, too. Never did watch all of TTGL here, oddly enough.
Every time Gainax does one of their "we're just unwinding and having fun" anime, good things happen. FLCL was a glut of experimental animated magic and Gurren Lagaan doesn't disappoint at all. Both are just plain great.
I've never looked at the Getter Robo series. If you haven't seen all of Gurren Lagaan, do yourself a favor and catch the rest of it. A lot of what's set up in the earlier episodes pays off toward the end. There's a certain bitter-sweetness to the final episodes as the characters get up in years.
TTGL's one of my all-time favorites. It's one of the few action series that doesn't stagnate (battle-of-the-week formula). There's progression and every episode is very different from the one prior.
TBH, most robot anime center around either some political struggle where there's a lot of down time OR it centers around a rivalry between the two best fighters of each side. TTGL doesn't do this at all and that's what gives it an A+ in my book.
It doesn't matter if the glass is half empty or half full. There's clearly enough room for more wine.
