Thank you, everyone. I have done a few of these things in the past--slow level progression, gritty realism, etc. Part of the issue is that I play on Roll20, so other systems are much less well supported. I appreciate all these suggestions! I really do like 5e as a system, but it plays a bit too superhero for my tastes as a DM. My players like it, for the most part, but I'm fortunate in the fact that my group wants everyone to be having fun, not just the PCs.
We have played the Free League Middle Earth game and liked it. We've played DCC which we all like. Dragonbane, too. Castles&Crusades is on the docket, but it's really clunky on Roll20.