We recently ranked Irrational Games' 2005 tactical shooter SWAT 4 as one of the best FPS games of all time. It was also, thanks to the vagaries of IP rights and the black hole of Sierra/Vivendi, very difficult to get. So it's a very happy surprise that GOG has added the SWAT 4: Gold Edition to its lineup today for $10.

The Gold Edition includes both the base game and the Stetchkov Syndicate expansion; the GOG release also comes with HD wallpaper and scans of the manuals—which are important, since SWAT 4 isn't your average run-and-gun shooter. At the head of a five-man SWAT team kitted out with the latest and greatest of tactical/military hardware, you must work within strict operational procedures, subduing and arresting suspects were possible, killing only when necessary, and avoiding civilian casualties above all else.

To celebrate the new availability of SWAT 4, GOG also posted a Q&A with lead designer Paul Hellquist and level designer Bill Gardner. They talked about the development team's commitment to authenticity throughout the game, and also credited it for enabling the development of another Irrational hit: BioShock.

"BioShock would probably never have happened if not for SWAT 4. Before that, The Lost had been a failed project and the team needed a big win. SWAT 4 allowed us to bond while we built up our tech and confidence," Gardner said. "We were all big fans of SWAT 3, but we saw a lot of opportunities for success and to put our mark on the franchise. The environments were quite sterile, for example, so that was a big opportunity that I saw. We used to say that SWAT was the one ray of light peering into a very dark world. We wanted to capture a lot of the same bleakness captured by David Fincher and movies like Seven, and I think we nailed that in lots of ways."

GOG also has the previous SWAT games, Police Quest: SWAT 1 and 2, and SWAT 3: Tactical Game of the Year Edition, on sale for 75 percent off—that's $2.50 each—until January 31.

Update: The post originally indicated that SWAT 4 on GOG sold for $12.50. That's actually the (currently discounted) cost of SWAT 3 and 4 in a bundle. SWAT 4 by itself is $10.