You may find many of the Activision titles still hold up. River Raid, Megamania, Seaquest, Frostbite. There's a lot of fun to still be had in those games, especially if you're competing head-to-head.
But for my money the most fun you can have on an Atari 2600 today is 4-player Warlords with well-maintained paddles.
My vote for River Raid, H.E.R.O., and Enduro. Cool fact that I only recently discovered: River Raid was designed and programmed by a woman, https://en.wikipedia.org/wiki/Carol_Shaw .
Carol Shaw is married to Ralph Merkle, of Merkle Trees fame, used in many applications, including git, Cassandra and many cryptocurrencies (including the original Bitcoin).
Yeah! 2-player (or 4-player!) simultaneous Warlords or Medieval Mayhem are really fun, even in 2022.
After many decades I finally managed to try it out, on a real CRT and everything. It's not something you generally want to play for hours or anything like Mario Kart... but it is really really good.
But for my money the most fun you can have on an Atari 2600 today is 4-player Warlords with well-maintained paddles.