CTF can definitely be fun in the right server. I had some really good CTF moments in the "Always Online CTF" server. But you very rarely see a CTF server anymore with a low ping that allows more than 16 people to join.
On small maps 16 is fine, but I always like around 24-32 to give it that extra action, if your computer can handle the extra processing.
The object of the game is obvious, the name tells it all, "Capture The Flag".