At times, it's sort of hard not to be with long-running franchises. Doctor Who, for example, is... I think it's turning 50 this year, actually - I was introduced to Series 4 of the reboot, but I've now seen all of that and am making my way, on and off, through the original series, from the beginning. I had never seen any Star Trek before the 2009 movie came out, and by before the end of the year I'd seen all the Star Trek there was, save Enterprise.
With video game franchises in particular, there's long, LONG-running ones like the Elder Scrolls, Final Fantasy, Zelda, where the originals aren't only so old that, for someone my age, I couldn't have been exposed to them at release, but their original forms are so technologically and stylistically removed from their current incarnations that being exposed to the franchise through the original is near impossible.
Doesn't happen for me with books, though - I'm careful to get the first book in a series - that way you aren't going to miss anything, it should all make sense. The sole exception to this is Terry Pratchett's Discworld, where although I did start with the first book, The Colour of Magic, I wasn't hooked until my friend gave me Men at Arms, which is the 13th overall and the 2nd in one of the many story arcs that make up the series. But hey, Discworld is pretty unique in that respect.
So yeah, while I am, rarely, hooked in by sequels, once I am I do my best to start from the beginning to get the whole story.
