[A Zarkin' Frood]

I recently purchased HeartGold. My last Pokémon game before that was Silver.
I haven't played anything in between, but the remake got updated by a good deal of features and gameplay mechanics (yes I hate those two words). But I find the gameplay as simple as ever. It might even be a bit more accessible to some thanks to the optional touch controls (As a lefty, I'm glad it's not forced on one)

The Pokéwalker is basically a pedometer you can catch some mons and find some items with. Nothing to be afraid of, and you can completely ignore it of you wish.

I think it wouldn't matter which game you get. As I assume the gameplay of the remakes got updated with the most recent additions (at least that's what my brother told me, who played some rubies, pearls and leaf greens.) The core gameplay is still the same, though. And the tutorial at the beginning does still assume you are braindead and/or never played a Pokémon game in the past.