PSASBR is a one off game... best without a sequel? Eh... IDK. There's some potential there, but a lot of really bad decisions.
If you'd count it as a one off title, Kid Icarus Uprising. It's not exactly a one off, but apart from the characters and plot it has really little to do with the other games in the franchise.
Codename S.T.E.A.M. is a game I love that was sadly underappreciated.
Eternal Darkness was great for its time (although it hasn't aged amazingly). Sadly the pseudo sequel never got off the ground, and with the issues with Dyack, probably nothing's gonna happen. Unless Nintendo wants to try and revive it... but I think maybe they should just leave it be.