If there is an asterisk(*) next to a feature, it means they fixed/added it in Platinum. If there is a pound(#) sign, it means it's a broken feature in Platinum.
In Diamond/Pearl
~*The battle speed could have been faster*
~Again, the same wild Pokémon appear throughout the entire game. Bidoof, Bibarel, Buizel, Floatzel, Geodude, Graveler... It got repetitive until Swarms came about. Then it got boring after I got all of those...
~The E4 Level Gap.
~*More diverse storyline. It was good here, but it really could have been better. Needed a little more of a challenge*
~Double Team on Staravia. It just pisses me off.
~Defog. Need I say more?
~*Gym Leader rematches would have been nice.*
~*SLOW surfing speed...*
In Platinum
~#Some Pokémon's front battle sprites lag between the viewing and the dance/cry.#
~#When "the other trainers don't feel like battling right now. Let's try again later." is displayed after using the Vs. Seeker, it lags.#
~#A battle against Charon would have been nice.#
~#A storyline that involves Looker a little more. He was pretty chill. I just wish there was a little more backstory on him, as well as a potential battle against him.#
~#Origin Forme Giratina was a bit of a letdown for me.#
~#Skymin only being available during daytime. Since I can't get Wi-Fi very well during daytime hours, I play at night. Shaymin/Skymin is part of my competitive roster.#