There is talk/rumours of a lot more being shown at the Future Games Show on the 25th. Or maybe access to the beta then as well.
Personally after playing the alpha i wasn't sure what to think of the game. The guns felt quite solid but the game also kind of felt like a mix of KF2 & L4D rather than feeling like a new kind of L4D. I'm sure the beta will have a lot of things that were not put in the alpha though.
Kind of annoying that there was no new L4D after the second game. They added quite a lot of content just 1 year after the first game came out. It just says to me that another 1-2 years later they could've practically made a whole new game even if it was with the same engine. L4D lacked content and enemy variety and L4D2 mostly fixed that for a little while. Shows how much more they could've done with a third game.