Excellent tactical shooter. Not as good as SWAT 3 in some ways.
In SWAT 4 you lead a team of 4 police men as you enter various locations to do the dirty work of arresting armed and dangerous criminals. The early missions are what I suspect are the usual SWAT situations where you have to arrest one or a few bad guys in their home. However, the dificulty picks up quickly and some of the later missions are more like warzones than anything else. Whatever happens however, you are supposed to keep your cool and offer everyone a chance to surrender. This is in fact what makes SWAT so special.
Compared to SWAT 3, a few things stand out. The AI of your teammates is much improved, so they are now at least able to stack up at a door and flashbang the room without exposing themselves too embarassingly. On the other hand a few nice touches of SWAT 3 are gone. Disarmed suspects no longer pick up their weapons and turn on you if you turn your back at them. Missions are less varied as well. Your fellow officers' inguries also never carry over to later missions, everyone is automagically healed in time for the next mission.
SWAT 4 introduces a substantial array of non-lethal weapons, but your teammates are hardly able to use them to good effect, and they are unable to forcibly disarm uncooperative suspects on their own.
Now on to the good: the graphics are highly detailed; all of the 13-ish missions are littered with everyday items, such as tools, cans, magazines, clothes etc. resulting in a highly realistic environment. The audio is particularly impressive, from the gun sounds to the very high number of spoken lines for the suspects that you arrest, it's excellent. New insults
Bottom line: if you're into tactical shooters, you'll have to get it.