...aaaand here's my chance to grump like a cranky old man about the one thing that I have YET to see a front end understand.
Every front end I've ever used comes with the inherent assumption that systems are self-contained and contain no crossover with any other system. I'll give you an example of where this falls. Pick a series-- wait, I've got one right here from earlier in this thread: Castlevania.
There's no way to tell any current frontend I've run across that, yes, Super Castlevania 4 is related to Castlevania on NES, which is also related to Castlevania Bloodlines on Genesis, and SOTN on PSX.
I'd love to be able to tag each of those games as "Castlevania series", then tell the frontend, "Hey, I'm feeling up to some CV. You mind showing me all the CV titles I have on here?" much the same way you can currently say, "Hey, show me all the NES games I have."