Problem #1: The "Whoops, this show's about the wrong person" problem:
Movies are self-contained stories. Even the biggest franchise is unlikely to reach more than 10 hours of total running time over the course of its existence. In comparison, TV shows are open-ended. The average television season is 22 episodes, meaning that for a 44 minute drama (16 minutes of commercials) you're going to end up with over 16 hours of programming in just the first season. This means that while in movies all the roles are written beforehand, and with the tight running time supporting characters have fairly rigidly controlled places within the film, TV is more flexible (The fact that television shows shoot while they broadcast is another factor in this.) In TV a likable supporting character can gradually get more screen time, a recurring guest role can be upgraded to regular cast member status, and the balance of attention can change.
To an extent.
The thing is, if you start a show with a certain premise you have to stick with it or you risk alienating your initial batch of viewers. So CBS' "How I Met Your Mother" has to be about Ted, even though he's the blandest character on any show in the history of television. Neil Patrick Harris' Barney can move from a small supporting role to a bigger one, but he can never be the focus of the show (Not that he'd make a good show necessarily. Certain characters work fabulously in small doses.)
Entourage has this problem. It was pitched as a show about 4 friends in Hollywood, with lots of neat swag and beautiful women. That show is kind of pleasant as "Wealth Porn" but not really that interesting. Vincent Chase and pals never really have any true conflicts. No matter what happens they remain rich, young, and swimming in pussy.
Jeremy Piven's character Ari Gold was originally in the show as a way of congealing Hollywood's legendary pettiness and deal making apparatus into a single character. And he does that pretty well. Except there's a problem. Jeremy Piven is a much better actor than any of the other four guys, and has a lot more charisma. In his hands Ari Gold is about 20 times more interesting as a character than the supposed main characters of the show. He was the breakout star, and the producers knew it. So they tried to compensate, giving Ari more screen time and more of a story, basically writing Debi Mazer out of the series for all intents and purposes to make room for him, and entwining his lives much more deeply with theirs.
But it doesn't really work. Because they have to keep the show about Vince & Pals to satisfy the core viewers (Who want to see success and all those TITTIES) and keep Ari ostensibly on the fringes. This leads to shows where you have a really strong storyline full of drama and humor and memorable moments, and then a really boring one about who's going to wear what to the party. This season Ari has faced the pressures of running his own agency while running out of cash, dealing with a vicious studio head and a spacey client, and developed an actually interesting human relationship with his wife (who is both controlling and supportive.)
Vince and pals have bought motorcycles, gone to parties, and dealt with an annoying houseguest.
Add in the fact that Piven is a strong actor while the other guys are not (Adrien Grenier is a pretty face with some charisma who can't quite be bothered to do more than read his lines. Jerry Ferrara is probably playing himself...poorly. Kevin Dillon hams it up as a character who hams it up, creating a hell of a lot of ham, and he sometimes struggles with his lines as well...and Kevin Connelly is about as memorable as a cardboard cutout. They tried to push him last season, but he's just bland in too many ways.) and you have a schizophrenic show that is entertaining but never reaches its potential. You also have a great character trapped in a show with a bunch of mediocre ones. Which is sad to see.
2) The Bad Premise Problem:
Another problem television faces, and this is mostly in terms of specials and TV movies rather than episodic series, is that it is often a dumping ground for premises and ideas that don't make the grade for film. And with bad premises, well, there's only so far you can go. I've been watching the TNT series "Nightmares & Dreamscapes" and there's a lot to like about it. It has name actors who are actually good ACTORS rather than stars (If you don't love William Hurt you don't love yourself.) It has good production values, and most importantly it has interesting direction and experimentation. In the first episode, starring William Hurt, there is almost no dialogue. The story is told visually, and told well (though a film would have better cinematography.) You can't do that in film today, audiences wouldn't get it, but TV is a place where you can actually tell a story through pictures. Unfortunately the story being told is supremely stupid. It's toy soldiers attacking a guy who killed their boss. I mean as a B movie it's an okay idea, but it just doesn't have what it takes to match everything else in the production.
And this is necessarily so. Because Nightmares and Dreamscapes are adaptations of Stephen King stories. And if a Stephen King story was good enough to reach the big screen, it would. These are the castoffs. And they're being done well, better than that Secret Window movie. But they're getting the B stories to work with. And that's not fair.
Don't believe me?
TV is still a ghetto when it comes to getting the top-notch ideas, even if it is no longer lagging behind film artistically.
* For gingerdevotion. Sex & The City has the same problem as Entourage did. Carrie is the least interesting character of the 4 women. Her character arc is the worst. Sarah Jessica Parker is not a good actress and is not particularly attractive. If you look over the arc of the series, you have 4 women in their mid-30s who conform to certain stereotypes and are living lives of fun in Manhattan. Over the next half-decade 3 of those women grow and change in interesting ways. Charlotte goes from a prim and proper old-fashioned girl who wants all the trappings of success to a divorced woman who has learned that people and situations should be evaluated as individuals and not how well they conform to stereotypes. She ends up with a guy who her original character would probably not want, a Jewish divorce lawyer who's a little bit crass and not at all WASPY, but who is much more present than the WASP king she thought was perfect. Miranda goes from an independent career woman to a married chick with a kid taking care of her mother-in-law in Queens. And she's happier for it. Samantha accidentally finds one of her young conquests is more than he seems and grows from that.
Carrie? She just stagnates and isn't much different in the end from the beginning. She still cares about shoes and fancy clubs and her "Writing career" (though she's a terrible terrible writer.) Yet the show's about her. Because that's how it started out. And that drags it down.
P.S. I was never a Sex & The City fan, I only watched it because it was on in the same bloc as Curb Your Enthusiasm and The Sopranos, but I can understand why it was so popular. I also think it was very smart of the show writers to have the characters arc out the way they did. In the end the show doesn't glorify the shallow shopping and fucking existence it starts with, but the women don't get their comeuppance of being miserable old hags (this is how Western culture treats most rule breaking women) instead they grow and develop and find new passions and people and end up happy but in ways they didn't expect. That's much closer to life, and a much better cultural lesson than either of the other possible endings.