https://www.youtube.com/watch?v=i7KvO1fp8HY

"One Game. Two sides. This is Enclave HD.

This classic returns to consoles for the first time in nearly a decade, and comes to PlayStation for the first time ever. Fight in a dual campaign during the Great War of Celenheim in this enhanced and upgraded version of the beloved medieval action combat game.

...

The award-winning original version of Enclave was developed by Starbreeze Studios and released in 2002 on Xbox, and 2003 on PC. TopWare Interactive successfully re-released HD versions on Windows, OSX, Linux, and the Nintendo Wii in 2012. Enclave HD is developed under license of TopWare Interactive and will arrive on Xbox One, PlayStation 4, and Nintendo Switch with upgraded visuals and SFX, an enhanced soundtrack with over 20 new tracks, remastered music from the original game's soundtrack, and more!"

Wishlist entry

"TopWare Interactive successfully re-released HD versions on Windows, OSX, Linux, and the Nintendo Wii in 2012."

Should be this release then, since that's the only one available, but what exactly is HD about it?
Does the original 2002/2003 release look considerably worse than the 2012 alleged HD re-release?

I don't think so, at least on PC. It's been too long since I played the original retail version, so can't say for sure, but I can see the console versions potentially having stuff like lower texture resolution or framerate etc., so a HD re-release might have a point there.

AFAIK, the main point of the re-release on PC was to add the Digital Deluxe Content and milk people for the Soundtrack (which you can easily extract from the game yourself). It really does not need a visual bump on the PC (still looks great) and judging from the trailer, it looks pretty much the same.

Either way, I definitely recommend the game to anyone. I love the character and armor designs in it and the soundtrack is great too. Would be cool if instead of rehashing the first game over and over, they'd start working on Enclave 2.

So those mentioned HD versions for Windows, OSX & Linux re-released in 2012 actually aren't HD re-releases but the original 2002/2003 ones with just the "HD" tag slapped on (for marketing reasons)?
Good on GoG for listing it as what it really is, then.

Still wouldn't mind having this real Enclave HD version release here as well, whenever that console-exclusive period should come to an end.