I don't watch very many TV series at all. I have watched all the House episodes, which I think are absolutely fantastic. It is a show I enjoy immensely and which is simply awesome. (If you haven't seen House I can strongly recommend it.) I then watched the first season of Heroes, but lost interest partway through the second season. (I found it too disjointed and drawn out.)

The only other series I have enjoyed is CSI. I have watched entire seasons of all three sub-series (Las Vegas, Miami and New York) and have always enjoyed them. The reasons I like it are as follows.

1. Each episode is independent and doesn't require knowledge of other episodes. This means that I can watch them whenever, and don't need to worry about watching seasons in order.
2. The content is interesting and well thought out. The plots are intriguing with clever twists, and often provide interesting insights into society.
3. The emotional content is focused mainly on the victims and people related to the individual cases, as opposed to the main characters which appear in every episode. I tend to form fairly strong attachments to the main characters¹, and this means that I don't take the show too seriously since the hectic stuff happens to characters that I don't know well.

However, I have just finished watching the eighth season of CSI Las Vegas, and I am very disappointed with the show. It has continually been breaking points 1 and 3 above, two of the prime reasons that I liked it so much. There have been (significant) recurring stories throughout the season, and the main characters have become personally involved in the cases, which has caused me to take it very seriously.

This has taken the enjoyment out of it for me, and since I watch movies and series to relax and unwind² it's no longer worth my while to watch CSI. I will continue to watch previous seasons, but I probably won't continue with future Las Vegas seasons.