The first piece of BioShock Infinite downloadable content is an arena combat mode called Clash in the Clouds. Available for $5, the DLC will launch around noon today on Steam for PC, with the Xbox 360 and PSN versions being pushed to their respective marketplaces as soon as possible (could be today, could be shortly).
At its core Clash in the Clouds is arena mode. Players gain access to four different maps, fighting 15 waves of enemies in each, earning varying amounts of money based on how they fight (headshots give a slight bonus, along with chain kills). Between each wave, players are able to restock. There are also "blue ribbon challenges," which require defeating a wave in a particular way (eg. shotguns only).
The cash earned is banked and can be used to open up items in The Columbian Archeological Society, which is the hubworld for the mode. Players can unlock and display concept art, character models, Lutece backstory Voxophones, Kinetoscopes and more. This trophy room is the highlight of the DLC.
From my brief experience with the mode yesterday, I was able to break it a couple times. After failing a blue ribbon challenge I decided to "restart checkpoint," but it turns out you can't restart a wave, so you'll be dropped back to the hubworld. After that I couldn't access the world and required a restart. After restarting I bought a vigor, which didn't show up in my menu.
Overall, the DLC features four maps, 15 encounters per map and a ton of unlocks for $5. It may not be the BioShock DLC that season-pass holders were expecting out of the gate, but it's good if you're looking for combat challenges in the world of Columbia. Burial at Sea is likely more in (sky)line with what season pass holders are hoping for.