|It still does.|
With the right writer-artist team, that's pretty much exactly how Deadpool succeeds. Those moments are preciously rare, alas.
Two recent Deadpool histories -- from io9 and the Onion AV Club -- portray a character who (like Harley Quinn) has a level of sass-appeal way beyond the ken of most stabled writers. Early Deadpool runs take him in one of two directions -- revealing some of the character's unexpected humanity, or inflating his "merc with a mouth" anti-hero status to absurd proportions -- crossing the Punisher with Spider-Man, basically. Either direction yields predictable results -- comic book (and movie) tedium.
Deadpool works best when he surprises everyone, including (one senses) even the writers and artists at work. Deadpool Dead Presidents is probably the best comic book example; the Deadpool video game is even better.
Beyond that I cannot and will not comment, except to say, Avoid the early Rob Liefeld material. Should you read (or subject yourself to) these stories, you'll not have the remotest idea of how this character could possibly appeal to anyone older than 12.