The entire verse is dived into 2 area: Its incredible power - Galaxy - sized mecha, true Big Bang level attacks, universal scale reality warp and threat,... and character's personality - many of them can be view as manly and epic, and GAR (although it's stated by 4chan member), but I wish the series last 1 or 2 more episode about Anti Spiral fight to explore more about the rest of Dai Gurren Dan's personality.
Another reason is Yoko, always wore "hot" outfit and make many people "nosebleed", and if you ask is there any hand-to-hand feat for TTGL, well the answer...is yes. Viral and Kamina are pretty much above peak human due the incredible fighting skill and stamina, endurability (like Kamina capable to survive a direct blow from a Gunmen of One of the Four King), Lord Genome are above 2 of them. There also 2 movies retelling the story with additional scenes and more epic fighting scenes but are non-canon to the anime.
The series is very great but mostly overrated by fan and cause hate to many veteran mecha fan, overall the series are massively powerful but nowhere near Digimon and Pokemon not be mentioned the higher verse. Lastly, for any remain fanboy of TTGL (If you have any objection, meet me at Mangafox on monday). The movies featured a more powerfull STTGL but isn't canon.
Tengen Toppa Gurren Lagann isn't the strongest and largest mecha, the title is belong to Demonbane (strongest) and Clockwork Phantom (largest).