First of: I’m not describing myself as a "Brony". Never did, never will. Because I think most of these people are the ones that follow every new thing and hype it up without really appreciating it. They’re buying the merchandise, being totally proud about themselves and after some time they hop on to the next popular bandwagon. Every fandom has their black sheep’s, but of course, most of the people are really cool and tolerant.
Why do I, as a 21 year old man like a show about ponies? Well, I always loved cartoons. I watched them as kid, I watch them now. And I know when I see a dumb and cheesy show, or an intelligent and well written one. My Little Pony is definitely the later.
I like the animation, the colors, the fantasy setting, the voice actors, everything. It’s such a fun and colorful world with a lot of humor. The characters are well written and developed; the stories are interesting and unique. It’s the first show that I watched in my entire life where I can truly say: That really is a show for the whole family. It was intended as such and succeeded. And because a family often has a grown man or big brother around, they are also a target audience. They get jokes and easter eggs that little kids can’t possibly understand.
Hell, I laughed so much at that show, because it’s just good old humor. It’s not that stupid sitcom humor that punches you in the face until you laugh out of despair, it’s really funny.
Yes, some episodes are plain, boring and a huge cliché. They feature themes that aren’t really intended for grown up man. Examples being: Modeling, wedding, babysitting.
But even these I enjoyed, because the show never abandons its style that I really enjoy.
I could write a lot more but I guess you get the idea. I’m a person with a lot of fantasy; I enjoy video games, comic books & cartoons. I’m not what a "grown up" should be, at least by society’s unforgiving standpoints. I never abandoned my inner child, I nurtured it.