Whoops, missed this thread.
Yes, I am hard at work on Pokemon Diamond right now. If you liked previous Pokemon games, then certainly get it... the gameplay is exactly the same. The graphics aren't much flashier - there's a hint of 3D in the environments, but it's essentially the same... the biggest difference is that it uses the extra space to incorporate *all* the elements previously unique to earlier games, making it an incredibly complex game if you want it to be (ie, you mix barries and there's weather and there's times of day and there are contests and there's an underground and there are secret bases so forth).
The multiplayer is amazing - I've been able to trade Pokemon and battle with Trelane with ease, complete with voice chat!
I'm taking it slow and savoring it -- I'm about 30 hours in and have four badges. My favorite new Pokemon so far is Finneon. I can't wait to get t o a point where I can transfer my other Pokemon to the game.