I've also ordered a copy of Akumajo Densetsu, known domestically as Castlevania III: Dracula's Curse. The Famicom version reportedly has extra hardware built into the cartridge, and it will be interesting to compare with my American copy of the game, provided the Japanese game works properly through the adapter.
One last comment: I've spent some time looking more closely at my Famicom copy of Bubble Bobble 2 and I'm a little suspicious that it's a pirate. Compared to Karateka, a game I figure no one would make the effort to pirate, it has a cheaper looking label and uses a different plastic housing. Anyone have concrete tips on how to tell pirate Famicom cartridges from the real thing? Nintendo's anti-piracy site doesn't appear to cover the Famicom...
Actually, there is so much variety when it comes to Famicom carts, you might never find out for sure. I used to own the Famicom versions of Batman, Dragon Spirit: The New Legend and Wagyan, and the Sunsoft Batman catridge was completely different from the two Namco carts, which was completely different from the Taito Operation Wolf cart that friends of the family had, and the Rockman 2 cart we borrowed from my little brother's friend was also different. If it helps, the Operation Wolf cart felt like it was made from lighter plastic and the label was more papery than the Namco games. Oh, try to get a Famicom if you can. The Sony sound chip in it is FAR superior to the generic one in the NES. Batman sounded good on my NES, but it sounded AMAZING on the Famicom.