Heroes, while it may not be as well-written as other sci-fi-ish shows (like Babylon 5), it still stands on its own as being an amazing piece of motherfucking ****.
The characters, you fall in love with. The conflict, keeps you guessing. The timeline, keeps your brain fucked.
It's an amazing show, and it also helps to bring the "geek culture" of comic books and sci-fi into the mainstream media, which was previously an alienated culture. Sure, Star Trek and plenty others have done that before, but Heroes changes the image that shows before it have left behind.
I love Heroes. I just wish the second season didn't suck.