If you want to shoot a load of armed-to-the-teeth terrorists, then Rainbow 6 Vegas is the game for you.
After spending some time in Mexico, you finally move into Vegas where you find a hostage situation taking place. At this point the Mexico part seems really pointless and just a bit of filler - and it is, really. It doesn't really add to the plot and so I think that it should not be in the game.
The gameplay is quite good, with a fairly standard controller setup that is relatively easy to use. The only thing I found annoying is having to hold down buttons while switching weapon or putting a silencer on your gun. It also uses a good cover-shooting system, which enables you to kill enemies from the relative safety of cover.
The graphics are really good but can get in the way slightly when you finally get to Vegas, where it's sometimes too bright to really see well.
In conclusion, the gameplay and graphics are really good but because of the almost-pointless Mexico missions, I'm only giving it a score of 8.5.