I never even knew Ubisoft released a HD Splinter Cell until today, and then I found out it is only for Playstation 3/Playstaion Network... That is a massive heartbreak, we need a petition for Xbox 360 Splinter Cell HD!
Ubisoft simply ported the first three games from the PC (and didn't include the COOP missions, any of the bonus missions, or any bonus features) and turned up the resolution a bit. Simply put, the Splinter Cell HD Trilogy was half-*ssed, just like everything Ubisoft does nowadays. You didn't miss out on much.
I'd love to see the trilogy come to the 360 as well (hell, even the other version of Double Agent as well), I want to be able to play those games again while in an XBL party without having to hook up another console and use up half of the city's energy to play in peace .