Waiting until the release of DEFCON in September may be best (if you don't already own Uplink and Darwinia) because they might have a package with all three at a better deal.
The painting in the control room where you talk to Viktor Radek and the hologram of Elexis Sinclaire, is really cool. I kept staring at it for a while.
maybe this gets to the whole reason why the combine invaded earth in the first place; they are tunneling down to cultivate the very power of the earth as an energy resource.