The Physical/Special split added a new layer of strategy and made Dark-types more useful.
The new evolutions, while controversial, helped underused Pokemon get an edge.
Some trade evolutions (Gengar and Steelix) can actually be found in the wild.
After being removed in Gen 3, the Day/Night system returned, and it has since become a regular feature.
The Battle Frontier is back and it remains a good postgame area.
The Underground is an expansion of the Secret Bases from Gen 3, and you can also get some rare items down there without having to pay any money.
Let's see here...
Gen 4 gave us one of the greatest One Piece stories lol, Pokemon Adventures Diamond & Pearl + Platinum Arc!
And by extension Pokemon Adventures gave us the best incarnation of Cyrus!
Dawn is an awesome addition in the Pokemon anime!
Gen 4 gave us the best Mystery Dungeon games!
Gen 4 gave us the best Pokemon Ranger games!
Gen 4 gave us Pokemon Battle Revolution, arguably having the best graphics out of any Wii game... wish I could say the same for the gameplay.
Pokemon Ranch, one of Pokemon Bank's predecessors came out.
Some of the best Pokemon movies!
... and still nothing about the Pokemon main series games itself lol.
The way of importing Pokémon from the Gen 3 games was much better than in Gen II and the fact you could make Pokémon hold items during transfer was a nice touch especially when getting more of the harder to find TMs in Gen IV like Iron Tail.
Heart Gold and Soul Silver were the best of the remakes in terms of content. ORAS come closet to that honor but fall short because they had no following Pokémon and no real post game after the Delta episode.
The night and day cycle was a welcome return and the fact that the music in several areas changed to suit the time of day was well incorporated.
-The physical/special split
-Sinnoh is my second favourite region
-The amount of postgame content
-The Gym Leaders, Cynthia and Cyrus are actually tough to beat
-Team Galactic is the first evil team I liked
-Torterra, Staraptor, Rotom, Togekiss, Floatzel, Gallade, Weavile, Roserade, Magnezone, Mamoswine, Palkia and Giratina-Origin
-The Battle Frontier
-You actually had to see every Pokemon in the regional Dex to unlock the National one in the Sinnoh games.
- Physical/Special split. It's income cannot be overstated.
- Evolutions to older pokemon. Yanmega, Togekiss, Weavile, Gliscor, and Mamoswine are some of my favourites. Mismagius and Honchkrow too.
- Day/Night cycle returns
- Cynthia is the best champion
- Best difficulty curve (Platinum)
- Mt. Coronet (the best "dungeon" in the series thus far)
The best soundtrack in the series imo
Really good Pokemon designs, including some of my all time favourites such as Garchomp, Roserade, Luxray, Torterra, Empoleon etc
Vast mountainous region that encouraged exploration
Strong (at least at the time), memorable champion with a cool and diverse team
Strong post game
Walking Pokemon is HGSS
Pokemon sprites were probably the 'cleanest' in the series
Gen IV gave us:
- the best remakes ever (HGSS)
- following Pokémon
- a new iteration of the Battle Frontier (even if not as good as the Hoenn Battle Frontier, it's still good)
- the biggest region sofar (Sinnoh)
Following Pokemon added immersion to the games.
They added a crap ton of new features on top of what was already available in the Johto games, such as the Pokethalon.
The game featured an "autorun" button that allowed you to run without the need to press a button.
They removed the "one transfer per day" limitation on Gen 3 transfers from the Sinnoh games.
The Johto Safari Zone and other new areas allow the player to catch some Johto Pokemon without having to wait until the Kanto section of the game.
The Battle Frontier, while copy pasted from Platinum, is still a good post game feature.
The addition of Wi-Fi connectivity and worldwide trading was the best way to get rare and trade Evolutions that players with no friends to trade with could use to finally get a chance to use a Kingdra or Alakazam.
The Special/Physical move split was the best thing to happen to competitive battling.
The best remakes were released this gen.
The game utilized the DS’s capabilities to the maximum and all of the gimmicks involving the touchscreen and GBA slot worked very well
Background music changing depending on the time of day set the atmosphere nicely.
I also enjoyed the Wi-Fi Plaza that was added to Platinum version, even though I felt that the concept should've been introduced in Diamond and Pearl. Still, it was fun to go there and play the mini-games, and it's too bad that we can never go there anymore since Nintendo Wi-Fi was shutdown for Gen IV.