In gameplay, there is a number of differences. I'll tell you, I have a great memory of Platinum. xP
- In Twinleaf Town, there are snow patches spread around the town.
- You have to verse Crasher Wake before Fantina. (Or, at least, one gym leader before another, anyway.)
- Half of the gym puzzles are different. (Crasher Wake, Candice, Byron and Roark have the same gyms as in DP)
- Nearly every city in Sinnoh has been changed, if it were the roads, the decorations, anything.
- Misdreavus is not present in the Lost Tower. (xD)
- In the Pokemon League rooms, there has been a bit more effort decorating them.
- There is a Distortion World you can access.
- Dialga and Palkia will be in different places in the Wayback Tunnel (or something like that)
- Pokemon's sprites have been changed a bit.
- Gym Leaders now have animated sprites.
- The trainer's sprite (overworld and face-to-face) changes
- There is now a BATTLE FRONTIER! :D
- The Pokemon League's Pokemon get tougher (-.-')
- A few more National Pokemon have been added to the Sinnoh Pokedex (more to catch! Happy rainbows xD)
- The little 'bars' in battling (you know, the bars that show the Pokemon's team, HP and EXP) are now black with white text.
- The star of the game is Giratina
- You get to rebattle the gym leaders and Elite Four.
Um... I know there's more, and I know I've gotten a little detailed. :P
Soz about that. I just miss that game so much. :')
Can't see myself restarting it any time soon though. Hm. ;(
Hope I helped. :)