It is difficult to love a book without loving the character. I'd go out on a limb to say it's impossible. When we fall in love with stories, we fall in love with the characters. If you don't care about the person, you won't care what happens to them.
So as writers, how do we create protagonists that readers care about? Here are a few suggestions:
Multi-Faceted. One of my biggest pet peeves is when the protagonist is a cliche, cardboard cutout: the tired/alcoholic cop, the sociopath with a traumatic upbringing, etc. Readers like characters with more than one dimension, especially when that dimension is one that you wouldn't expect: A killer who's very religious and goes to confession after every murder or a cop who dreams of becoming a folk singer and plays at cafes and local open mikes. Readers want characters who are more than just their job title.
Baggage. There's nothing I love more than a protagonist with a past. We all are who we are and are doing what we're doing because of past experiences. Let your character carry some baggage and show readers how it affects their actions in the story.
Goals. All of the characters in your book should have goals, but your protagonist's are the most important. Clearly illustrate what their goals, don't let them achieve them too easily, and make them driven and passionate about reaching those goals.
Conflict. A character without problems is a character without a story. A book cannot simply illustrate a character on a journey to achieve their goals. There must be conflict, problems, obstacles.
Flawed. Perfect characters are boring and not believable. Characters with weaknesses and flaws are more interesting and realistic. Giving your character a weakness will not only make them more believable and sympathetic, the weakness will also serve as an obstacle to overcome.
What should you avoid?
Cliche. Both in dialogue and the characters themselves.
Gimmicks. Sometimes they're funny, but more often then not, they're cheesy. Unless you're Monk or Elmore Leonard.
Forcing a protagonist. Finding your storyteller should be organic; you shouldn't force the story on a character just because their convenient. Before you begin to write, brainstorm and look closely to find the true storyteller in your book.