>>25074230Well for Gen 3, it introduced a more varied region. Not hating on Kanto and Johto (which I like as well), but to me they are pretty simplistic regions (though they do have things that stand out). Hoenn on the other hand has a more varied landscape compared to the first 2 regions.
Plot related (I know, Pokemon doesn't have the best plots, but I still enjoy them), Gen 3 was the first game that introduced the "evil team(s) uses Legendary Pokemon for their goals" formula. Sure, that formula may have been overdone to death in later generations, but around Gen 3 this concept was new for Pokemon. I could also go into mechanics but I think that's obvious.
Now on to Gen 5, which is mainly plot related. It may not be the best plot ever, but it has to be my favorite plot in the Pokemon games (minus the Pokemon Mystery Dungeon games). What I liked about it is that it questions the morale of catching Pokemon. Is it the right thing to do? What I also liked is that it actually changed a thing about the "8 Gyms, beat the Champ" formula which every main series Pokemon has. It may not be much, but the Champion not being the final boss I think is really awesome.
All and all I like Gen 3 and Gen 5 the most because they tried to be vastly different then the other Gens in my eyes.