Really that boils down to the main issue with Deadpool, which is that he isn't that funny. Sarcasm is the lowest form of wit, apparently, but worse is being self-referential for the sake of it. Deadpool commenting on being in a comic book, breaking the fourth wall and interacting with the audience, is a neat idea that is never used to its full potential. It helps the reader and creative team feel smart without actually doing anything clever or funny. Part of the problem there is that Deadpool is most often written by comic book writers, not comedy writers. And there's a reason comic book writers don't do stand up. Writing a comedic character is totally different from most other stuff in comic books, especially when he's the lead instead of just the humorous relief that pops up every so often. Plus, half the time when a comic writer is trying to be funny and it's not in a Spider-Man book, it comes off as hackneyed and corny as a recycled Three Stooges bit. And, admittedly, sometimes it is a recycled Three Stooges bit. The aforementioned recent Deadpool run has benefited greatly from Brian Posehn writing. He's a comic book novice (in terms of scripting, anyway; he's a huge nerd going way back), but has decades of experience in writing and performing comedy, and that shows. He knows the timing, the taste of decent humour, and that really works. Most other Deadpool comics? About as funny as a frat boy reciting a half-remembered Dane Cook routine. In fact, there's a lot of similarities there. And Ryan Reynolds might look a bit like Cook, but he's better than that material.
Tom Baker is the Comics Editor at WhatCulture! He's heard all the Doctor Who jokes, but not many about Randall and Hopkirk. He also blogs at http://communibearsilostate.wordpress.com/