According to Entertainment Weekly:
http://www.ew.com/ew/gallery/0,,20336031_20342707,00.htmlUnlike movies, it appears that sequels to video games are just made to be "built upon". You have all the general ideas and, in some cases, sophisticated enough graphics that can be reused or simply tweaked (such as characters, scenarios, etc). A focus can be made, therefore, on expanding your original ideas. This is unlike the movies, where you essentially start from scratch with each new film.
(Btw, I'm enjoying
Mass Effect 2. Never played the original, but love the sequel. Same goes with
Uncharted in all respects...never played the original but loved the sequel. On the other hand, wasn't that big of a fan of
BioShock and therefore am not so interested in the sequel. The visuals were stunning, but the game itself just didn't grab me. To each their own!).
(Btw Part 2: Some of the best "sequels" I ever played were the
Ultima games. Thought the first (yes, I AM that old) was decent enough, but
Ultima II, which I played in high school, absolutely blew me away. Years later, at which point they were up to
Ultima VI or so, I revisited that game and couldn't believe how...primitive it was compared to what was out there. I know Ultima became an online experience, but haven't really followed it since that point).