I still play Diamond occasionally, but only for training. Last year December I completed the pokedex with the exception of the event type pokemon unfortunately.
I really regret not buying so many more DS games in Japan. At the Book-Off second hand stores (which are EVERYWHERE) Diamond or Pearl were only 200 yen while Pt or HGSS were 500. I can't believe not buying more. Not ideal if you're someone who doesn't read Japanese though. Similar deals on GBA games, while 3DS were more around 2000-3000. Look at the conversion rates to your own currency and be amazed.
I just beat cynthia in platinum. EASILY the hardest champion to beat. Now I'm heading to the resort area to my villa
Anybody who has a 3DS and an old 4th gen game, hell yeah!