I actually had the opposite happen to me when playing the classic Fallouts. I played Tactics first, and its interface and mechanics are so much more advanced and enjoyable to me, that when I tried playing Fallout and Fallout 2, I just couldn't stand the way they worked... and I really regret doing that.
Yeah, I know that feeling too. I think that it's harder to go from new to old if the difference in gameplay/mechanics is too extreme.
I didn't get on with any original Fallout games having come to them from 3/NV, although that's quite a big change in style (isometric turn-based to 3D FPS).
I still felt uncomfortable with Morrowind, coming from Oblivion/Skyrim though, which is less drastic a change. But I think I could persevere with it though.
But each person will obviously have their own limits for how different a game can be before they can't enjoy it.