Is it the genre, the opening theme song, the character designs etc?
I'm curious as to what lures you into watching an anime.
I am personally lured by cool opening and opening music and from there on I just watch the rest of the anime.
For instance the H-game anime Green Green TV, I usually don't watch hetero fanservice anime, but the opening was so cool I stuck with it...the anime was pretty funny too so that helped.
Here is the opening
::Warning Suggestive::
Paranoia Agent also was an anime that attracted me by the opening sequence and it turned out to be pretty damn good.
PS: I didn't find a similar topic, but my search skills fail so cut me some slack if its a repeat.