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It's your turn to defend Earth.

We always knew they might not be friendly. Now they are here and we must show them we can be pretty unfriendly, too.
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The 75% discounts will last until June 5, 10 AM UTC.
igrok: 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.
enkayeff: I did a bit research to confirm. The GOG release is 1.4 - the telltale deep death groan used for the Sectoids, Floaters and Snakemen is one of the trademarks of the 1.4 patch. Universally hated by most players who recall the original sound samples. The executable file sizes also match 1.4.

A quick dive with a hex editor later and I see GOG has also fixed the one byte that caused the infamous difficulty reset bug. This bug wasn't officially fixed until the PSX and Windows (aka Gold or CE) releases and had to be patched manually. Either way, bravo.
Thanks a lot for the helpful info igrok and enkayeff! It's much appreciated. :)