Castlevania: Order Of Ecclesia
I recently busted out my DS lite and gave Castlevania: OOE a whirl. I bought this game on release and played it during every lunch break for a while, but never beat it. I remember the mermaid boss being a major sticking point. It's pretty tough, but it's fun and the graphics are awesome. There's a record hidden in the starting area that allows you to switch the background music to the OG Castlevania theme.
For me, this is definitely a back and forth farming/grinding deal. Glyph drops are rare, and you probably won't collect them all your first pass through an area. While you are rescuing villagers and other Castlevaniay things you can also rescue cats and return them home. The SFX are pretty goofy and the humor, when present, is equally goofy. Very enjoyable.