First and foremost, Splinter Cell Conviction will feature plenty of daytime sneakery. Also, Sam Fisher will be spending a lot of his time navigating crowds, similar to Ubisoft's upcoming title, Assassin's Creed. It seems Sam has left Third Echelon -- for real this time -- in order to save Anna Grimsdóttir, his former coworker. New to the series will be "hero instinct" which allows Sam to sense enemies, displaying them in a manner akin to infrared vision. There is also a danger meter which displays how likely Sam is to be spotted by the enemy. Close combat is receiving an upgrade, which Pelaaja compares to the "Bourne" series of books and movies. We'll note -- as does Joystiq -- that it sounds like Sam won't be quite so stiff this time around. Furthermore, Sam can kill terrorists and mercenaries, but will only be able to incapacitate guards and civilians. Finally, Splinter Cell Conviction will have a revamped physics engine that allows players to utilize their environment more effectively. One example given is using furniture to block doorways.
All in all, it sounds like Splinter Cell. Hopefully, Conviction will add enough to the formula to keep veterans coming back and pique the interest of newcomers (and lapsed fans).