II - While I do think that this gen. was not as creative as the others, Gold, Silver, and Crystal are still the longest games in the series and has given the most gameplay improvement compared to the other Gens. It has also felt the most like true sequels. Ex. eggs, gender, hold items, character gender, new types, shinies, evolutions,
IV - So far it has not gone as far as the II gen. (thanks to the III gen.), but it has given wi-fi, the best story line, the most (and coolest) legendarys yet, and so far has had more competive play then past gens. Battling wise however, has done nothing to improve upon it. Plus the upcoming remakes of II gen. gives this Gen. a lot more going for it than the previous Gens. before it.
I - This Gen. has had the biggest impact over, not just the entire series, but the world. Period.
III - While I enjoy this Gen. a lot, and has been the longest lasting in terms of the number of games. It has done really nothing to help move the series along. Having to rely on remakes and mediocre spin off games to keep going, has only set series backfarther. The only good things are the new natures and ability, which has only made gameplay harder. Also, no one even likes pokemon contests.