Along with the highly anticipated Heavy Weapons Guy update, Valve is adding an Arena Mode to Team Fortress 2.  According to the developers, Arena matches are designed to be shorter, ending whenever one team wipes out the other or the central point is captured by either RED or BLU.  It's the closest TF2 has ever come to having a "team deathmatch" map.

Speaking of maps, Arena Mode will come in five explosive flavors.  Two of these maps, Lumberyard and Ravine, are completely new while familiar settings Well, Granary, and Badlands have been extensively revamped to suit the new mode of play.  The (or "A") Heavy Update site provides excellent descriptions for each new map, detailed as a tourist's sightseeing guide:

Lumberyard has an unbalanced structure, with one half of the map climbing up towards a large mountain peak, while the other dips down into a valley. A series of rooftops at the map’s center serves as the key battleground area, with lateral flanking being the key maneuver at ground level. When the capture point becomes active after 60 seconds, multiple entrances open up into the central control point, which becomes the focus of the fighting as the match nears its end. Lumberyard is one of the few Arena maps without water, and contains only a single health kit. The kit sits on a log above a deadly pit, making it a great ambush spot for Pyros, Demomen, and Soldiers to send unwary enemies to their deaths.

In contrast to Lumberyard, Ravine has a far more open ground level with emphasis on control of four key choke points. A series of canals in Ravine’s lower level provide an excellent opportunity for stealth kills and flanking maneuvers. Like all arena maps, the capture point in the middle becomes active after 60 seconds.

It may be worth noting that Health pick-ups are limited in TF2 Arena, and some maps won't have any Health packs at all.  This makes the game more challenging, and the Medic may become an even more valuable asset alongside Engineers, who can construct Health dispensers.  Water is also scarce in Arena, so Pyros might get to have a little more fun than usual. 

That being said, the maps are also designed to give each class an area to dominate, ensuring that no one is left out or forced to play a class they dislike simply for the sake of victory.