Do protagonists need to be likeable? A flawed hero is one thing, but an obnoxious principal character can be a challenge for the reader. I happen to enjoy central characters with less-than-pleasant personas, but many readers either want to identify or picture having a coffee (or a beer) with the fictional friend.
Like-ability is the issue.
On television, prickly characters always have a soft/loveable core. The experience of inviting the characters into your home (via your eyeballs and a screen) seems to require buffing the rough bits off until the character is easy to like. Yes, there was DEXTER and HOUSE, but they are the few losers in the Miss Congeniality competition among lead characters on TV.
Mystery fiction has produced some ornery protagonists. Some of these characters grow easier or nicer or simply less peculiar when they become the central figure in a series of books, as opposed to one-offs. Some of these characters grow on the devoted reader despite their difficult natures. My cat is named Morse after Collin Dexter’s Chief Inspector Morse. I don’t expect the cat to do crossword puzzles in ink, love opera, drink beer and continually fall for the wrong Kitty, but when he hid behind the refrigerator the first few days in my apartment, I knew he had a Morse-y side.
Still for every Morse, Dexter, House, Hercule Poirot, etc. there are many candidates for Miss Congeniality in serial fiction. Who is your favorite un-like-able character?