He didn't die.

Though I can see why people missed that, what with it being in episode 17 and all.
All in all, I enjoyed the show. I was satisfied with this ending. As a symbolic story of a girl going through puberty and reaching adulthood(Senketsu, you bro!) it worked rather well.
It's been some years that I actually watch a series as it comes out, normally I just watch after it's done. The last one was Fate/Zero, and it was more because I just wanted to see how they're gonna do it, since I already know the story.
I really find the characters to be likeable, but if I have to choose, the Four Devas are what keep me going and to me, Gamagoori Ira is the best character.
If we are to bring TTGL, then he's Lordgenome(also my favorite).

They even did the same "Achievement" that is only unlockable during the Final Boss Fight:
- Have a cool entrance
- Scream something with ''任せてもらおう'' (Leave it to me)
- Beat the crap out of whatever you are opposing
And they both use whip and burst out flames. No wonder I find him so amazing. Definitely the best moment for me in this last episode.
As for Ryuuko's final form,
.
Seriously people, what's with all this "super saiyan" and "super sonic"? Did you forget the greatness that is
Nono, Buster Machine 7? Is the color scheme not obvious enough? For shame!
One thing that I also liked for this anime is how they use vocals as BGM. It's not easy to make it blend with the scene since most times the vocals will get drowned or overshadowed the scene. But I think Kill la Kill did a good job on this part. It sure was a pretty fun experience and I'll remember this show.