Playing through the hard mode, which can be infuriating if only for the fact that some really annoying enemies can do waaaaaaay too much damage, and that the heal spell is a little disappointing.
Still a fun game.
Castlevania could benefit from a few changes for the next iteration, if it lands on the DS:
1) More dual partner stuff (motorcycles, pushing, etc) if that system is continued.
2) Ability to write notes on the map. It's hard to remember all the "Why did I continue there?" rooms when you gain a new ability. So being able to write "need double jump" or "can't push this out of the way" notes would be pretty awesome. Basically just an extension of the little feather markers.
3) Not letting me sell equipment I have equipped. That's just stupid.
4) Continue the quest system, but add more elements to it. Maybe it plays more directly into the story of the game, can alter the endings on a higher degree, gives you more worthwhile items.
5) Less useless equipment. Either give me more meaningful stuff or throw out a lot of it.
6) Make the actual castle the star of the game again. Less warp points, less save rooms, less empty corridors, etc. Throw in a TON of enemies. For inspiration, watch Vampire Hunter D, and pay attention to the first time D goes into Count Magnus's castle. I want enemy swarms like that - where they are crawling all over each other and such. If you're not going to update the sprites that much, at least placate me like this.
7) Fix Charlotte's running animation. Looks too stiff.
8) Maybe include (and I doubt this will happen) a better hub system that includes surrounding areas. I.e., maybe you can venture into a town outside the castle, and then a forest near it, and caves. Almost like Castlevania 2. But only do this if the main castle gets better treatment.
I guess that's it. These are the ramblings of a madman, but I still wanted to say them.