Quoted By:
1 was awesome, it was fresh fun and kicked the whole craze off.
2 expanded on it in every way and had tons of new features
3 was good, it wasn't as big a leap as Gen 2 but the quality of the whole thing was excellent and they still added lots of good new features such as abilities.
4 was a huge disappointment. It was so slow paced from battle to surfing, it had a terrible interface, it kicked you off your bike in gate houses and there were just so many things about it that were incredibly frustrating and made it a chore to play. There were some good mechanical changes such as the physical special split but it just felt broken, lazy and unfinished compared to Gen 3.
Platinum and HGSS fixed a lot of the issues from Diamond and Pearl and those are actually pretty great games, but DP left a sour taste in my mouth that will always make me remember Gen 4 as a disappointment.
Gen 5 is great, lots of smart changes to the interface, reusable TMs, phenomenons, the new register menu and just convenient smart additions everywhere. The region design was clever, the story was handled better than before and in general it was a breath of fresh air. Gen V was the kind of jump in quality I expect between Gens.
Gen 4 felt like Gen 3.5 and Gen 5 is what Gen 4 should have been to begin with. Overall Gen 4 is the most disappointing Gen of Pokemon.