The inherent problem with most tv show tie-in games is that the game is made and marketed as an extension of the show's plot, essentially reducing the target market of said game to people who watch the show. In turn, this leads to said game being allocated a low budget due to low commercial expectations which leads to a bad game, since they blow most of the budget on attempting to get the show's cast together. The Lost game made the sin of reuniting some of the cast, then getting lazy soundalikes for the rest, and it came out less than right. As for current tv shows as games, lets examine why not:
1. Heroes - In game, how would you explain how to limit their powers? For instance, if playing as Hiro, what would be the explanation for not being able to teleport wherever/whenever the player wants? If playing as Nathan, what would the explanation be for not being able to fly anywhere? It just wouldn't work. That, and nearly everything post season one has been utter shite.
2. Battlestar Galactica - My favourite show on television, so why not a game? A game, I feel, would focus on the space battle sequences which, while awesome, aren't the focus of the show. The show is about the remnants of humanity struggling to survive on a seemingly endless journey while being hunted by a merciless enemy. Although a level where we get to play as Sam and shoot Gaeta in the leg would be pretty frackin' sweet.
3. Firefly - What would probably be my favourite show on tv if not for the cancellation, but still not game material. The focus of Firefly was the crew of Serenity and their relationships with one another as opposed to action and shootouts, so the game would have to have a hell of a lot of dialog in order to replicate the feel of the show. That, and reuniting the cast might prove quite difficult as a few of them are ff doing other things. I want to see the story of our Big Damn Heroes continue as much as anyone else, but a game isn't the right way to go about it.
4. Doctor Who - Same principle as Heroes. It would be hard to explain why he can't go wherever/whenever he wants in the TARDIS. And it's hard to make an action game of a person who never uses weapons.
That's it for now. Might think of more later.