I was always hesitant to try it, I love the outdoor games, and am not afraid to be hit up close, Flag Raiders gives you plenty of that if your aggressive, I just preferred out to in. Then a good group of guys started hosting CQB games a couple years back so I tried it, and had a pretty good time. I find it for myself personally, a good once in awhile thing, 90% will still be outside.
Keys to CQB are to have a light, fast target aquisition sight, and make sure the gun is shooting where you are aiming. I use black bb's inside for that very reason, sight in outside with white, then your pretty much assured that wherever your sight is, your going to hit. Either armor up 100%, or as much as you need, full face is a definite.