Would be nice to indicate that it requires X11 in the System Requirements field. It's also conveniently missing from the product homepage.

I spent 15 minutes trying to work out why it was just sitting there doing nothing when I clicked Connect, then in desperation manually ran ./rdesktop, giving me a bunch of X11 errors. If it won't run without X11, I pass.

I'll just continue running my two sessions by using two copies of Microsoft's RDC.