Xevious 3D/G is an odd one. I play it again every few years, always to discover that it is somehow simultaneously more and less interesting than I remembered.
Raiden Project is always a good choice. R-Type Delta and Einhander are also worth a look if you haven’t tried them.
And don’t miss Harmful Park. It’s been a while since I’ve last tried to get someone to play that game with me, because it’s been a while since I’ve interacted with other humans in general.