Legacy of Kain. For me, a lot of the strength of that series comes from its characters, narrative, and lore. The complexity of the narrative I think would function best as a TV series instead of a movie.

Diablo. Conversionly, narrative is not this series strong point, with it usually being very simple and broad. However, I think it does have some effective world building that could be fleshed out in narrative format and lots of interesting enemies and abilities that could make for great action sequences. I think it could be similar to the Castlevania anime series in this regard, though this could easily function as a fun action movie as well.

Starcraft. I'm just a big fan of these games and the narrative, particularly with Brood War. I would love an adaptation of this series that would focus more on the politics, the backstabbing / profiteering / desperation felt within each of the various factions and in their dealings with others, and on the few heroes within each that are striving for real change. Game of Thrones, but in space! Starcraft 2 took a nosedive in this regard by making their story far too broad and abandoning these flavors by instead shifting a lot of focus to an all powerful, all evil entity, which is pretty boring in comparison (and also infuriating since it stripped agency from previously interesting characters, but this isn't a "Starcraft 2's Story Rant" thread, so I'll stop.)

Final Fantasy XIV. I think this game already has a very strong narrative, so I don't think a series would be successful in just outright adapting that. However, there are also some incredible world building in this series with a lot of fantastic settings and characters. They would have a myriad of options here. They could have an apocalyptic type movie set in the past depicting the leadup to and the result of the first Final Days as shown in Shadowbringers, a series depicting the beginning of the Dragonsong War and going even further if successful, a series focusing on the conflict between the Eorzeon Alliance and the Garlean Empire, and many other possibilities. By its nature, the story of the game is tied directly to the player character, but I think an adaptation would be wise to break away from this and instead focus more heavily on other established characters (or even new characters), by either omitting the warrior or light angle entirely or just making them another major character amongst a large ensemble of major characters. The game already does a pretty good job of showing the viewpoints from and even sympathizing with each side of a conflict (though not necessarily condoning the actions taken by those sides), so any adaptation should make sure to at least match that level of examination.

This isn't quite on topic....

But I would love it at the end of the FF7 games, if Square can remake FF7 Advent Children movie where they update the graphics visuals and character designs based off the new games. The current FF7 Advent Children still looks great for its time but I think it can use a facelift to match the new games.

I would like to see an animated elder scrolls adaption.