Here's a brief listing of some of the television shows I watch, and ones in which I've lost all interest. Castle starring Nathan Fillion.
This is my current favourite show. I always get the feeling that not only do the actors have a blast with the show, but the writing staff is having an absolute hoot. There are so many writing jokes in place, and other geeky references, especially with the character of Rick Castle. I can't see anyone other than Fillion in this role.
Big Bang Theory
A bunch of extremely nerdy theoretical physicists and engineers, with many geek pop references. While some of the characters are more than a little out there, this is a refreshing show. Also, as this show is lacking in the blood and gore, unlike most crime shows, this is appropriate to watch while my toddler is still awake. I love the reaction when Sheldon receives a napkin signed by Leonard Nimoy. Classic.
I've recently started watching Doctor Who, starting with the 9th Doctor, and have now watched all of the released episodes. It's playful, fun and very entertaining. I really appreciate the ability for the lead actors to switch out when the Doctor regenerates, as it allows the show as a whole to remain the same, but shift significantly in tone. The latest season, with Matt Smith as the 11th Doctor is an excellent example, as the entire tone of the series shifted from David Tennant's seasons. Part of this was also due to the changeover of the writing staff, as Russell T Davies passed the reins over to Steven Moffat.
After watching Doctor Who, I started watching Torchwood. Far more adult content than Doctor Who has nightmares of. I'll say this: If Joss Whedon and Russell T Davies ever collaborate on a project, kiss your favourite characters goodbye, because guess what? They're going to die. If they're like Captain Jack Harkness, they're going to keep dying again and again.
The Mentalist starring Simon Baker
This is another show which has a prominent lead actor. Baker puts forth a strong performance, and it's always interesting to watch his antics. It does get a little formulaic though, and there isn't near the amount of comedy.
Lie to Me starring Tim Roth
This bears some similarity to The Mentalist, as the lead character in both shows has an uncanny ability to read others. Lie to Me seems more gritty and grounded in reality. Perhaps this is due to the setting in Washington, rather than Mentalist's California setting.
This is more of an ensemble show than most of the others, although Mark Harmon's Gibbs is a fantastic lead. The show would be severely lacking if any of the main actors were to depart. Abby, the goth lab tech fills me with glee.
CSI used to be one of my favourite shows, and while I appreciate Laurence Fishburne's character, the show is not the same without William Peterson.
Another show I love to watch is PBS' Nova. A great deal of very interesting science. The different specials often have great interviews with leading scientists, such as the wonderfully amusing Neil deGrasse Tyson. Thankfully, he's in a number of them.
I used to watch House, with Hugh Laurie, but it became less interesting as the seasons developed. Too often, it devolved into strange disease of the week, without enough character development. Also, when it focused on characters, House is just a jerk. It's part of what makes the show what it is, and the attempts to actually change his character just ruined the show for me.