Psst...
The game sticks to the formula of the first two (Splinter Cell, and SC: Pandora Tomorrow) but differs in slight but significant ways. For example, there are primary, secondary, and opportunity objectives. Only the primary objectives are the ones you have to complete, the others add to your overall "score" or success rating at the end of the level. Also, three alarms no longer means that you've failed. It just means complete your Primary objectives then get out.
The sound in the game really adds to the atmosphere, with excellent music written by an electronic artist named Amon Tobin.
Definitely check it out.