I built this for a project last year that never completed. A fairly large layout, consisting of an outdoors start area, leading into a base. Nothing special, but it's a fun battle that should take around 30+ minutes.
ID Software, for DOOM.
A couple months.
None known, but I didn't test every source port. There are no :"special effects" that might cause problems with GL ports, :but if you use any model packs, the tree sprites will :obviously not work.