It depends on what you’re playing, really. I just could never in good conscience recommend an online shooter as a way to release tension. It’s too unpredictable. You go in thinking you’ll get some headshots in and end up getting frustrated because you got killed three time in a row by the same sniper. Seen it happen too many times.
I would recommend one of those crazy single player shooters if you really want to shoot something, something along the lines of Bulletstorm or Half Life. Any game where you’re overpowered enough that you can go crazy and not end up killed by a headcrab.
Or go play something zen. Something with an instant reward, like bejeweled infinite mode, or something like that. Platformers can be very fulfilling in that regard, so Mario or Kirby are good picks.
These suggestions are a little out there but I think I made my point.
Videogames offer enough variety that there is at least one out there for every situation. Just go play something fun!