Hey... Don't you think that these place should be filled somehow? It's kind of a waste of space. Maybe the game's rating could be there? or some description, tags?

Don't you know wasted space is latest trend in UI design? The more wasted space the more modern your site/app is.

For GOG's next trick, all the dynamic game logos will be replaced by flat colorless vector art.

As a UI UX Designer I don't see an issue with the example you provided. Cluttering is also a bad thing to do, only things that are important should be shown.

I disagree with your view: one person's clutter is another person's useful/important information. The space could be used for an optional description (e.g.). Like an icon that shows more (in-place) when you click on it.

I like "modular" UIs, not minimal (or contextual) ones that treat everyone the same (often as an idiot and/or very inexperienced person).

In short: "modern UI design" is often based on popularity, not usability. It's understandable, probably cheaper to implement, but IMO far from ideal.

I think they made a good point that the ratings are not visible anywhere on the gamecards.

Hmmm... If you could tell it tags or things to show up there, that could be useful. Say common tags (point & click, RTS, visual novel, etc) perhaps other things like year it was released, if it uses DosBox... but it would have to be configurable to your personal viewing to be the most useful otherwise it would just be a clutter, a wall of text...

Easiest for that would be if every game included all that information, and then the browser on your end would filter it via JS, that way there's far less to manually pull per game and thus be more efficient server-side... Though most tags can be a heavily compressed portion of 8 bytes or so to decode to 64 different types of tags/meanings.