Seriously you can't get better value for money than at least the first three games.
The only other games sold here are probably the Civ games.

Get 'em!

Uh GOG, the sale is not in the header menu. What's its point, then? Might and Magic 1-6, HoMM3 Complete, Quest for Glory 1-5, either Neverwinter Nights.

This is perfect timing, the last few days I'd been thinking about adding the first two X-Com games to my GOG collection, those were next on my list to get, now I can afford them earlier than anticipated at this reduced price. Thanks for the generous sale, those games are between my top all-time favorites! :)

Admittedly I've never played an X-COM game before, but they look quite nice. I've been feeling a bit of space intrigue lately considering trying out a Mass Effect game to see what the hub-bub is all about. They just seem so daunting with the amount of time to pour into four games.

Beautiful. I'm glad I was able to grab these.

Oh, you mean you disagree with me? I found someone on the internet who disagrees with me! Shocking. :p

Terror from the Deep was one of the first PC games I've played, and it still holds its own. And for anyone worried about the original UFO and X-COM's bugs and limitations, I really, really recommend openXcom - it's easy to install, and has a ton of QoL features, to say nothing of the vibrant modding community.

Bought again, it's one of these cases...
Still waiting for OpenXCom for Apocalypse.
Meanwhile - heavy taxing and booty collecting with army of stronk mutant women.

A great game series. Kind of odd that it is on sale and you have to click on individual links to each individual game though without there being a single "click here to see list as a bundle" type page like most sales have. That would encourage people to buy more of the games I would think, but what do I know about marketing. :)

If you go to any one of the game pages, you can choose to grab them all as a bundle (it's under the individual game 'Add to Cart' button). Then you can grab all at once, or remove any you may not want.

Similarly, TFTD/Sweet memories of mine.

The game is fine as long as you are aware of a couple of game engine/program limitations. The 255 items is the most important. Too lazy, just google it.
The game is perfectly fine to complete it without worries. I never ever had issues with the game since the original floppy disk version. Apart from one crash and I believe another time in the early 2000s when I couldn't make it run properly on WXP or W98, I don't remember.
As with all games, make sure to have several save game slots, just in case.

The one I haven't experienced any issues ever in 20 years is Apocalypse. But I am sure someone will reply here saying the game is almost unplayable because of bugs, or something...

It is still somewhat buggy. GOG's version is 1.2. The latest official patch was 1.4, but I think it mostly addressed some issues with sound card support. The game was never completely fixed (well, long time ago I also played the version for Sony PlayStation and didn't have any visible problems with it). It's not as bad as the 1.0 version of the game (which had many problems), but it is still possible to encounter certain bugs (like the same battle reloading all the time - I had to consult the bug list to fix that). But game breaking bugs are very rare.

Some issues in the game are mostly annoyances that can be avoided with experience (e.g., when aliens attack one's base, the game picks the worst combination of available equipment for the player).

To sum up, it is not 100% bug free, however, one can play it, complete it and have a lot of fun.

It is much more polished but also much more challenging. I really like it though, it is a fantastic game. I would still start from the first game, however.