The initially centers around Simon (Kakihara Tetsuya), an expert digger in an underground village. He's a little weak-willed and cowardly, but, being underground, digging is important and he's the best as it. He's looked after (and dragged into trouble) by his self-appointed "big brother" Kamina (Konishi Katsuyuki), a hot-headed, ridiculously self-confident man, who is bent on making his way to the surface. One day, Simon discovers a strange little head with arms and legs while digging, but also gets locked up with Kamina thanks to their plot to escape the village. Then, the vault over their underground township breaks open and down falls a giant malicious looking mecha, which looks like a large mechanical head with some smaller appendages, followed shortly by a scantily-clad, rifle-wielding woman named Yoko Littner (Inoue Marina). In the panic, Simon and Kamina discover that Simon can somehow pilot the little mecha head, dubbed Gurren, and they destroy the threat and make their way to the surface with Yoko, where they discover that the beastmen have been oppressing or eliminating the humans that attempt to live on the surface. And so begins a journey to make the surface inhabitable by defeating the beastmen and their Spiral King. Or so they think...
The overall series has a two-part structure with each half being predictably tonally different, with a more fun and lighthearted first half and a much more serious second half, bridged by a recap episode right in between (by the way, I hate recap episodes). Overall, the series has the simple theme of the hope, drive, desire of the indomitable human spirit, originally embodied in Kamina, which effectively spreads to the other characters. Despite the light-hearted nature of the first half of the series, it doesn't hold back from tragedy and our main characters will see a large share of tragedy before the end of the series, but I appreciate the emotional depth afforded to most of the characters, even as Simon threatens to fall off the boat of caring due to his intense whiny angst a quarter into the series. But he gets better. And the series gets increasingly epic, to universe-threatening levels, a feature found in a number of fantastic science fiction oriented series like Gurren Lagann. Fortunately, the pacing for the series is pretty tight and while there are slower more anthology-oriented episodes, no episode is wasted in terms of moving the overarching story along, especially insofar as it explores the themes as embodied by the different characters that are introduced throughout the stories. The ending fortunately avoids the fate of being a total mindscrew and leaving everything unresolved as Gainax has been known to do, so in that sense, it's a wholly satisfying watch.
And this production is very clearly a Gainax production, boasting absolutely gorgeous art, whether it's being fun, funny or aiming at ultra-cool mecha combat goodness. Like the story, the design aspects are often heavily exaggerated to proportions (especially the size of the mecha Gurren Lagann's drills) that would be laughable if it weren't just so ridiculously awesome at the same time. Likewise, Gainax's non-stop love of fanservice is present in the super-skimpy string bikini that Yoko sports without a reason or a rhyme. The artwork style also follows the first/second half division in the story by presenting goofier art in the first half and much more intricate and serious designs in the second, without losing the link between the two.
Ultimately, Gurren Lagann is a wild ride. While the story is plenty predictable, borrowing from the larger tropes present in its boy-oriented mecha genre anime, its willingness to just go with its guns and embrace ridiculousness with gusto turns it from being stale exaggerations of the genre to awesomely fun, even if the overall story is simple. And the simple story has merit, making a statement about the power of (not necessarily religious) faith, but not in simple terms, showing both the boons and the losses of a life led in the pursuit of greater things. Tengan Toppa Gurren Lagann, then, is everything it aspires to be: one heck of a good time with giant robot battles, shonen-styled melodrama, wacky characters and serious characters, and a willingness to go overboard for the sake of cool. And in its genre, that's better than a lot of its peers can even aspire to. It's not a transcendent work, but it easily earns its praises by providing heaps of fun. Good stuff for people that like boy-centric anime. 8/10.
Note: I only had the opportunity to watch the English dubbed version and I will admit that the voice acting, especially early on, was quite uneven and sported the same cast of voice actors you hear doing practically every English anime dub ever. I wasn't terribly impressed overall, but it wasn't bad enough to be distracting, although the mixing into the rest of the soundtrack did leave the voices seeming unusually flat. I'm curious to see how the original Japanese soundtrack sounds.