I think I've probably stayed away from the CSI franchise because it has so many spin-offs and I'd be tempted to jump into all of them.
Oddly enough, while I love the original CSI, I haven't been at all tempted to watch any of the others. Because while I like the show concept, it's the characters that grabbed me, and since those characters aren't in the spin-offs, they feel enough like separate shows for me not to feel as if I'm missing out if I don't watch them.