Anyone who's read the many reviews for Diamond and Pearl will have noticed one consistent thing-the games are being criticised for being essentially the same as the previous games in the series, only with a graphical upgrade, more Pokemon and some added features.
I'd say I have to agree with them. While, yes, D/P are the best games in the series since G/S/C (R/S/E didn't work for me, but LeafGreen I say was the best third-gen Pokemon game I ever played), they aren't really different from anything that's come before them, except for the aforementioned changes.
Now I'm wondering exactly where the series is headed if those are all the changes that the developers are going to make. If the eventual fate of the Pokemon series is to end up with over nine thousand (sorry, couldn't resist) Pokemon species and a battle system so refined it's insanely complicated, then I'm probably going to sign off being a fan.
Even though I'm basically complaining about the 'sameness' of these changes, there are some I do like. The physical/special attack split for one was a brilliant way to make some Pokemon better, and it did make sense to have the elemental punches run off the physical attack stat and Hyper Beam to be special. The Underground is the best new thing ever invented in the series, giving people more to do than just trade, battle, and participate in contests (Hell, I've wasted more hours down there than I have battling my friends), and I sincerely hope it returns in the inevitable future games.
But what now? The battle system is refined enough already-to mess around with it more would be tantamount to making bagpipes into string instruments; it'd mess it up. EVs, IVs, Natures, and all that rubbish are making my head spin like a leek. Do we need any more complications?
Of course, there ARE going to be new Pokemon-just because they made the Pokemon equivalent of God doesn't mean they're going to stop anytime soon. Yes, there are billions of animals they haven't Pokemonified yet-swordfish, dolphins, mata-mata turtles, Heilan' Coos, bombardier beetles, whale sharks, zebras-but when the new sets inevitably have the same (or at least some of the same) things-useless rodents, three-stage bird families, evolutions and pre-evolutions of old Pokemon, etc.-they repeat themselves.
In conclusion, Pokemon seems to less concerned with being innovative and providing a fresh experience with each new 'main' game as they are with reissuing the same formula with shiny graphics and tons of extras. That may be fine for now, but I doubt that it'll keep them up forever.