Pro There is actually quite a bit of macro management
It looks like just a point and shoot game from the outset, but outside of the motion and aiming, one needs to also manage their amount of money, and of course work with a team. On top of this, one needs to get a feeling of the maps and the players' locations.
Pro Fun team based gameplay
If you want to win, you need to have good knowledge of the map (know how long until an enemy may arrive, at which point, etc), predict enemy moves, and arrange with your team how to deal with your mission. This includes coordinating formations, grenades, and of course avoiding friendly fire.
Pro Requires insane reflexes and senses
Pure aim is very important and requires lots and lots of practice. Then there is not only aim, but also handling of various weapons and adapting to the range and weapon of your target (so you can't just point and hold the trigger). This also includes having to rapidly switch aim and throw a grenade, and switching to aiming a weapon, getting over, and instantly switching to a knife if surprised while reloading.