It adds a lot of multiplayer game types: Harvester, Overload and One Flag, all focused on team play. There is a selection of new power-ups aimed at introducing a class-based structure similar to Team Fortress. Three new weapons are available: a nail gun, a chain gun and a proximity mine launcher. There is also a batch of new levels, and a few graphical and sonic tweaks like the inclusion of Doppler-shift effects when rockets streak past your head. And finally there is a set of one-use items like Kamikaze (kills you in a colossal explosion, taking out anyone unfortunate to be around) and Invulnerability, which freezes you in mid-air and surrounds you with a near-impenetrable shield.
One of the clans in Quake III: Team Arena, The Strogg, is also an alien race in the Quake universe; they are the main enemy in Quake II and Quake 4. The names of three members of the clan, Enforcer, Icarus and Paracyte are also the names of three enemies in Quake II (the last one is called Parasite there).