I never played these games back in the day, so apologies if this sounds stupid.
I adore both UFO: Enemy Unknown and Terror from the Deep - is this similar but sans aliens and with more AK-47s?

Awesome, well I'll give it a go then! Going to grab this and Fallout Tactics as I haven't tried either. Cheers!

I'll have to agree with Reavan. I've been playing Jagged Alliance since it's first incarnation in the early 90's, and grew up playing X-Com. Both games have a place in my heart as the finest tactical squad based games. Hopefully GOG will get Jagged Alliance 1, or JA 2 Gold. Both are well worth it. The personality of each of the mercenaries is incredible, adds so much depth and you develop attachments (or despite.. haha). Great fun all around. Also there's a very active community developing custom mods for the game (New weapons, characters, etc...).

I am a fan of X-Com and I fish GoG added those Ufo games here too.

Steam offers them for a similar price--I got them there. Runs very well under dosbox.

This is where we see the difference between Steam and GOG.
Steam made no changes to Xcom to allow it to run, as far as I'm aware. And it shipped with a TINY disclaimer to the effect that it wouldn't work under Vista. I didn't see that till I'd purchased it, assuming, like an idiot, that if it was being released on Steam it would run on contemporary systems.
No such luck. Can I get a refund? Can I hell - this is Steam we're talking about.

GOG rules vs. Steam, you'll get no arguments from me there, but UFO, TFTD, and Apocalypse all run perfectly for me under both Vista and Vista 64. I've played several complete games of UFO and Apocalypse (very very happily I might add!!!)
They are the original versions but they use DosBox, they're not the problematic Windows port CE versions that I could never make run right. Sound (except for low pitched alien screams, for some reason), video, everything is perfect and they run at the proper speed. If you're having trouble getting them to run you might be able to find help on one of their forums?
That said, I would buy them again from GOG in a heartbeat if GOG offered these games.

Ditto. I actually still have my original XCOM UFO Defense disc from the 90's, but I don't want to bother with DOSBox and command-line prompts. I would be thrilled to buy the XCOM games here at GOG. Tell the truth, that' and Fallout were why I joined. I thought I had heard they had XCOM already.

Oh yeah, I'd buy them in a heartbeat! I loved all the X-Com games and I do hope that GoG will get them soon. Like most of you I also grew up playing those old games. Fallout and JA2 were the reasons I joined GoG. Gotta call my cousin to join and break out the old joystick and get some Descent action going too!

I got stung by Steam's X-Com too! The crazy thing is I had the games anyway with the bootlegged patches that enabled it to run, but I bought it from Steam to make sure that:
A) There were royalties being paid and ...
b) So that it would run without these hacks.
Still, I'm sure GOG will get them soon enough (and make them work properly)! If anyone needs these patches just go here: [url=]http://www.xcomufo.com/[/url] as it contains most of the stuff you'll need for all versions.
As for JA2 being like X-Com yes they are in terms of combat, but there is a much more involved storyline with JA2 which I like, but it can get a little bit in the way (unlike X-Com's evolving storyline based on the research that you were doing). Some people will much prefer having such an involved RPG though so I guess that's just my take on it.
Anyway, I'm so glad that this site exists and already it looks like a decent community is building up!

wittzi, you're probably referring to steam's initial release of TFTD, which was the CE version and not vista compatible. yesterday, steam released a patch that changes TFTD to the DOS version (like UFO and Apoc) and it now uses an optimized version of dosbox to run. as others have already said, all of the X-COM games released by steam are fully compatible now.
all the steam releases of the X-COM games use the latest patches, too -- TFTD even comes installed with the 2.1 beta patch.

Uh, guys...if and when X-Com is released by GOG, it will run in DosBox, like all the other DOS titles offered by GOG. I have played Steam's DosBoxed version on four different computers (all various flavors of XP) and it works fine on all. I have the original game too, and was never too successful on getting it to work as smoothly as the Steam version did.
I'm not trying to start a Steam vs GOG war here. Steam is a great, established too. GOG is a new tool, appears to be fairly solid, and I have no complaints about the service at all. I expect to use GOG for older games, just happened to find X-Com on Steam first.

A bit off topic here, but this is an issue with how the Collector's Edition handles the sectoid's death scream. There's a patch for it here
Here's the source
As for JA, if you liked Xcom's missions, you'll love Jagged Alliance. Unfortunately the administration part is not that good, but it makes up for it by giving the mercs a great deal of flavour!