Fantasysci5: I'd ask if Hitman 2 is a good starting point if I've never played any of the series...but I get the feeling I'd get a lot of "BUY IT RIGHT NOW!!!" comments... ;)
I just wrote some of my thoughts about the Hitman series.
http://www.gog.com/forum/general/half_the_sleep_twice_the_fun_insomnia_returns_to_gogcom_64aad/post337 The game sale ended so I've got no agenda to make the game sell faster (and am going to bed very soon), although it will likely appear again a few times throughout the promo so if anyone missed it they can probably have another chance at it. I do recommend getting the entire Hitman series, whether all at once or individual promos over time, and I think the best way to play is one game after another in chronological order, but I'm a bit of a completionist too. They're fun to play either way though. I'd say keep your eyes peeled for any of them coming up on sale and grab them all as they show, or get the ones you can now anyway. :)