Action Quake II has a variety of game modes, as listed here.
Action Quake II was originally a deathmatch mod, with realistic weaponry, weapon effects and locational damage. In general, players are spawned into the map with a weapon in hand and the goal is to kill as many other players as possible before a time limit or frag limit is reached, whereupon a new map is rotated in and play begins anew.
Teamplay (TDM) is a round-based game mode, where players join one of two teams and battle it out. Players choose a weapon and special item, and may change those choices at any time, but that choice will only go into affect in the next round. When one team eliminates all of the members of the other team, the are awarded a team point. Matches generally end when either a roundlimit (team points) or timelimit is reached. This was the precursor to Counter-Strike's round-based system.
This mode is identical to Standard Teamplay, but with another team added to the mix. This changes the dynamic of some map strategies and can be a lot of fun.
This mode plays very similarly to Standard Teamplay, with the exception that the team points are awarded based on successful completion of a scenario. Players also respawn periodically, a fixed amount of time, if a certain amount of members of the team are dead, or instantly. Scenario types CNH, CTB and OFC are continuous play, as in there's no 'end' to a round until the roundlimit or timelimit is reached. The others types rounds end when an objective is met.
In this mode, there are two teams, Red and Blue. Both have a flag on the map, and they need to take the enemy flag and bring it to their own to score a point. (Capture the Flag, or cap for short) The other team will attempt the same. To prevent spawn camping, there is an invulnerability/shield mode to give some people some protection.
Darkmatch has 3 modes. In it's first mode, the map will be pitch black, except for certain lights. This means that players have to be careful where they walk as they do not know when they will walk off a building. Also, firing your weapon will make you show up clearly.
In the second mode, the map is in it's near black mode. The map will be very dark, and it will allow for more stealthy play.
The third mode will simulate a real day. The map will go from normal lighting to pitch black and then back again to normal lighting.
To assist players, there is a flashlight available in darkmatch only. When used, it will create a circle of light at wherever you point, but it will also light you up, making you an easy target.
The newest game mode added to the suite is Domination mode. Very similar to Espionage's Capture 'n Hold, here there are fixed flags (typically 3) scattered around the map, and touching a flag will claim it for your team. Keep control of flags to score points; your team gains 1 point per flag controlled every second. The score limit is 200 per flag in 2-team mode, or 150 per flag in 3-team mode, which means a typical 2-team game with 3 flags has a score limit of 600.
Matchmode is a special form of Teamplay, made for clanmatches. It has several features which can be usefull during matches and league games. It makes sure the whole timelimit is played.
Clients will have a few more things to do during matchmode: they have to have a captain and substitutes. Everybody in a team will only be able to talk to his/her own team, with the exception of the captain. Subs are players who are part of the team but aren't playing at the moment. With limchasecam enabled, they will be limited to viewing their own team.
For those who want to offer a Rocket Arena style one on one server, this mode is ideal. It will let two players spawn and face each other. The winner will stay for the next round and the loser will go back to the queue. The winner then takes up the next player in the queue.
Example: There are 4 players on a server, A, B, C and Z. Both A and B play each other, C and Z are in the queue. B wins and A gets put back in the queue (which then is C, Z and A). Then, B plays the next in the queue, namely C. If B would win, he'd face Z and C would get put back in the queue. If C would win, he would play Z next and B would be put back in the queue.