The main cast of Glee is certainly an eclectic bunch. As the show's primary themes are accepting differences, embracing personal problems, and coming together for the good of friends and enemies alike, the cast is composed of a wildly different group of characters.
Some of these characters are very likable, and they make watching Glee a pleasurable affair. Other characters aren't nearly as likable, and while they may be entertaining as fictional characters in a television show, they certainly don't prove good people (or good role models). The diversity in question helped make Glee such a relatable and enjoyable show.
Sue Sylvester
Sue Sylvester is the clear 'villain' of the show, and is generally not a good person. She certainly has a few admirable qualities, and the show often went out of its way to make Sue a more sympathetic character. But while the depth was much welcomed (and necessary), it doesn't change the fact that she is routinely rude and selfish.
She often bullies the students, is openly rude to their faces, and often makes fun of the Glee club's inclusionary efforts. She has a few good traits, but she is by far the least likable character of the main cast.
Rachel Berry
Glee took a major risk in making Rachel Berry its primary protagonist because she isn't very likable. She isn't on the same level as Sue in terms of abrasiveness or rudeness, but she is still a very unpleasant character. Like Sue, she is openly rude to others.
She is also incredibly selfish, she thinks far too highly of herself, she hogs the spotlight at the expense of others, and she is wickedly spoiled and entitled. It got so bad that some fans didn't want her to succeed. She has her good points, of course, but could have used a little more humility.
Santana Lopez
Santana Lopez was one of Glee's strongest characters in terms of depth and complexity. She could prove incredibly rude and cold to others, but as the show suggests, her abrasive personality is a defense mechanism to keep people away and prevent them from getting too close to her. This becomes even clearer when she comes out as a lesbian.
But complexity aside, Santana could still prove a very unlikable person - especially in the first two or three seasons when she served as the resident bully who wasn't afraid to make fun of literally everyone. Thankfully, she mellowed with time.
Quinn Fabray
Like Santana, Quinn proved one of the most complex characters in the early seasons of the show. She begins as one of the primary antagonists, serving as a spy within the Glee club while allying with Sue and the Cheerios. Luckily, the Glee club helps Quinn through some of her personal problems, and she quickly finds herself with some genuine friends.
Quinn is quite a cold and emotionally distant person, but not to the rude extent of someone like Santana. She's neither good or bad, but she's certainly not unlikable.
Mercedes Jones
Mercedes is certainly one of the strongest singers within the Glee club, rivaling the likes of Rachel and Santana in terms of pure vocal prowess. But on a personal level, Mercedes could often prove a little difficult. She wants desperately to be seen as a coldblooded diva, and she acts suitably diva-ish.
Unfortunately, divas do not often make for nice or agreeable people, and neither does Mercedes. With that said, Mercedes was perfectly likable when she wasn't trying so hard and just being herself.
Noah Puckerman
Noah Puckerman is often seen as the "fun" member of the Glee club. He begins the show as an antagonist, fully committed to athletics, being "cool", and making fun of the so-called losers of the Glee club. However, he later learns to embrace the fun and healing potential of the Glee club and soon becomes its wackiest member.
It never seems like he "belongs" with the Glee club, but that's exactly what makes him so endearing and endlessly enjoyable to watch.
Artie Abrams
There's nothing much to dislike about Artie. Unlike the other characters so far mentioned, Artie doesn't go out of his way to be rude, confrontational, or unlikable. Rather, he's arguably the most passive member of the Glee club.
He just wants to sing and have fun with his friends, and if his friends need help in their personal lives, he's there to lend a hand. He certainly has his flaws (like treating Brittany quite rudely), but for the most part, Artie is one of the true good ones.
Finn Hudson
Like Puck, Finn begins the show as a "cool guy" devoted to athletics and football. If it wasn't for Schuester being in the locker room, it's possible that Finn would have never joined the Glee club. Even after ingratiating himself within the club, Finn often battled with the two sides of his personality, resulting in a brief departure from the Glee club to play football.
But he means well, and he's one of the kindest and most mature characters on the show. So mature, in fact, that he let Rachel go to New York without him and later took over the Glee club from Mr. Schue.
Will Schuester
It's almost impossible to dislike Will Schuester. The man begins the show as a sad character, regretting his life choices and appearing as a washed up and aging performer who squandered his potential. These traits helped make Will a deeply relatable character and a fantastic entryway for older viewers who might not have otherwise watched the show.
He also encourages everyone to follow their hearts and meet their potential, and he is incredibly inclusionary, welcoming all walks of life into his Glee club. His adorable dorkiness certainly helped.
Kurt Hummel
When it comes to the OG cast of Glee, it's hard to find a character more likable than Kurt Hummel. Kurt begins as a very pained individual, finding it difficult to fit in at school and facing hostility from his traditional and conservative father.
He seeks comfort and acceptance within the Glee club, and it makes him a very relatable. His personality is also very welcoming and likable, and he proves one of the kindest and "warmest" souls on the show. Any scene involving Kurt is a treasure.