What do you like about TMNT?

To be totally transparent, I'm a songwriter, and I'm writing a theme song for a fan project. My friend is a fan of the 2012 theme and sent that to me as a reference. The project director also gave me some direction such as Leo is the leader Raph is the hot head etc.

I have a few questions. What characteristics would you attribute to Splinter, Shredder, April, and Casey?

Also, what do you like about the show/movie/comic/these characters/storyline? My friend says he likes the character dynamics.
Is there a theme/heart of the show? Positive messages? I assume it's wholesome and light hearted with action?

Here's what I know. Radio active ooze, mutant ninja turtles, lives in NYC sewers, Shredder bad, Splinter is the mentor/father figure. April is a journalist and Casey is an ally who fights with them?

Basically, feel free to ramble, I just wanna get a better sense of what fans love about the show.