I'd love more games like the original Pokemon Trading Card Game on Gameboy. Going around, doing card battles, collecting booster packs for more cards after winning battles, building decks from the cards you earn, etc. I still enjoy going back amd playing the original Gameboy game from time-to-time.
I think I just mostly miss the aspect of earning the booster packs from winning battles, rather than having to drop money on booster packs with the modern games.
(Also, the soundtrack was awesome.)