After playing through the abortion that was Blacksite: Area 51, Midway's next-gen remake of 2005's Area 51, which itself was a reboot of the original arcade light gun game but in first person perspective, I was disgusted by it's horridness. I had fond memories of the both the light gun version, I'm a sucker for light gun games, unless the Menacer gets a hold of you, and the PS2 version of 2005's Area 51 starring none other than David Duchovny and Marilyn Manson. So I'm creaming my pants a bit to know that the PC version of Area 51 circa 2005 is available as a full version download for free seeing as it was arguably the best of the bunch and free games are always good, unless you're Blacksite, then a quick slap on the wrist and a waving index finger gesturing a fierce NO, NO, NO! are in order. Although it's ad supported I doubt it'll be anything that would make this not worth downloading, plus it's a little dated so if you've recently upgraded your rig it should do a decent job of keeping up with it.
It's available from Big Download, so get to it. Unless you like a good work out, I suppose you can get in your car, head to Gamestop and see if they a have a copy balancing out a table in the back somewhere. Yeah that's what I thought as well.