[Have on Steam] Considering that I own these already on Steam, I don't think it's worth buying them on GOG too.

welp, close enough

They are all old 2D arcade/console games from the Neo-Geo platform (released in 1989 and retired in early 2000s), except for a couple of the newer King of Fighters games. People of a certain age have a fondness for those games. Basically if you went to arcades in the 1990s you probably knew these games. The hardware was very similar to Sega Genesis/Megadrive but the games were huge, very expensive and had great sound and graphics.

Most of the games were fighting games as it was the era of Street Fighter 2 and Mortal Kombat and fighting games were the big games of the era.

There are also some run & gun games (Metal Slug series), shoot 'em ups (Pulstar, Blazing Star), a top-down shooter (Shock Troopers), a beat 'em up (Sengoku 3), and a baseball game.

As post above mentions, these are older, mainly 90's to early 00's games (except for KOF XIII).
If you like old-school fighting games, or side-scrolling run & gun games, it's worth getting some of them.
The Metal Slug series are a fun challenge, 2D side scrolling run&gun games (even more fun playing local or online co-op - I personally played MS3, and it was great).
The King of Fighters series are a solid 2D fighting game, much like the old Street Fighter games, but known for their cool 3-on-3 system.

There's also a mix of beatem-ups, shmups and top-down shooters in there, as well as many more fighting games.
Some of the other games are bad ports of the original games, or are a bit "weird", especially if you don't have any nostalgia for them.

If I had to recommend 5 games to give ya a bit of diversity, I'd go with:

1. KOF XIII (this is a much newer game than all the others in this bundle, originally released in 2010, so is more accessible)
2. KOF 98 -OR- KOF 2002 Ultimate Match ...or a non-KOF game... Garou -OR- Real Bout Fatal Fury 2
3. Samurai Shodown V -OR- The Last Blade (both weapons-based fighters)
4. Metal Slug 3 -OR- Metal Slug X
5. Blazing Star (side-scrolling shmup).

Anyway, I hope that helps.

Alright, thanks stlpaul Mayanaise for your help!

Hi, I didn't find (anyone can correct me, if I made a mistake):
Sengoku 3
Blazing Star
The King of Fighters 2000
Samurai Shodown II
King of the Monsters
Fatal Fury Special
Pulstar
Real Bout Fatal Fury 2: The Newcomers
Ironclad
Art of Fighting 2