Rainbow Six Vegas holds up really well on the PSP. It is easy to see that the game was designed specifically for the PSP since everything filters right in without the usual hiccups usually seen in system's steady stream of ports. Environments are well-designed and detailed; the only problem is that it completely misses the "Vegas" feel of the 360 version. Although the game takes place in Las Vegas, you spend an unusual amount of time outside the city. Rather than shoot-outs in casinos and the strip, you spend time in airports and other mundane areas.
Sound has always been important to the series, so it is good to see that the same attention was put into the PSP version. Environmental sounds lend a certain ambience to levels while random chatter from terrorists adds a little life. You also have a mission op feeding you data throughout missions. Gunfire is varied; each gun has its own distinct report, so you can usually tell what someone is packing.