Oh yeah, exploring different tones, settings, systems, etc can be really interesting! I usually listen to more lighthearted things, so I don’t have a ton of recommendations, but you might like Dungeons and Randomness.

It’s changed a lot since it started. In the beginning it was a pretty standard fantasy themed actual play between some friends, but has evolved into a pretty big living-world style campaign with several different groups of players. The tone starts out a little silly –e.g. there’s a magic item called the “gravy boat of pestilence” – but over time becomes much more serious. They start to deal with some fairly portentous themes, and some might even describe the tone as “dark” at times.

If you check it out, I recommend skipping the first two episodes entirely (they’re almost irrelevant to the larger story and they feel a lot less polished). From episode 3 there’s some plot relevant stuff, but you could safely skip up to episode 16 or 17 (at which point there are already two adventuring groups) and you won’t miss too much. If you want to get straight into the higher production value stuff, there’s a recap after episode 200 (the first “arc”), at which point there are four different adventuring groups. I wouldn’t super recommend that personally, I think there’s a lot of good stuff in the first arc, but I’m pretty sure they do recommend doing that. Up to you, of course.