According to some on the steam for Linux forum, Ubuntu does not show the right file size.
On openSUSE it was an 11.5 gig download.
I just looked with my file browser, the folder is over 18 gig.
So they used some compression tool.
The normal windows size is probably smaller.
This beta is not just left for dead 2, its a reworked Left for dead 2, which will replace the old one, when they are done beta testing.
In your windows steam library there should be two left for dead 2, the beta and the old one.
What they exactly changed, I do not fully know.
Last night noticed something though. The conversion and warnings are changed. First it was boomer, now I heard fat guy.
I would need start it on windows to really compare, but I believe they tweaked the graphics too.
Fire looked better, and I saw more ceiling tiles fall down.