>>50756126You know anon, I appreciate you askin'!
I have played every mainline Pokémon game, and what it comes down to for me is whether or not I would enjoy replaying the game in the present. Of course not every game is created equal, but I can say there isn't a single generation I wouldn't like to replay on account of the fact pretty much every one of them has something for me to specifically enjoy really no matter how many times I've played (as long as the gap of time since I last played said games is long enough). I mean it's one thing I got to experience them for the first time. That was novel and awesome, although some games I enjoyed less than others like X/Y and even Red/Blue. But I've found that coming back to really ANY of the previous games I've played there is always something neat I can do that I actually haven't even done before most of the time!
I recently completed the Pokédex in Crystal (and mostly in Fire Red) for the first time. It was a great nostalgia fest and I really got to completely dive into everything the game had to offer that I didn't as a kid.
Then I did the same for Emerald and even got to take on the Battle Frontier after training my bros. Of course I got to do the same for Platinum, although I'm actually not done with either frontier yet! =)
Then the Unova games I again worked on the dex, took on the post game facilities like the Hollow Tree, etc. Even X/Y I found really enjoyable working on the dex and collecting the mega stones, something I never did when it came out.
I could go on, but the point is even if I replayed those same games AGAIN in 5-10 years, there would still be a great sense of nostalgia and explorative wonder to be enjoyed. In fact I'm thinking about linking up my gen 1 and 2 teams to Stadiums 1 and 2 next time I play them. I love making new teams every time I play and making more impressive save files each time!