Ignore the reviews saying the game is corrupted, Ubisoft refused to remove the DRM, it is not Steam's fault.

You can easily get an executable without DRM in the game's discussions page. If you want this to be fixed spam Ubisoft or just get the fixed executable.

It's the first Rainbow Six game but you're playing through the events of the movie, The Sum of all Fears. Domestic terrorists steal a dirty bomb from the Russians, blow up Baltimore's stadium during the Super Bowl and your job is to figure out what the ♥♥♥♥ happened by shooting them, collecting intel, saving hostages, etc.

It does include a more streamlined campaign, there is no planning phase. Other than that though, it is the exact same game with mostly the same mechanics. If you like either Rainbow Six '99 or the first Ghost Recon, you're going to enjoy this.