Pokemon - Diamond Version Immediately

Compared to the other Pokemon games in the series, I feel that Diamond and Pearl are relatively lack-luster.
This group in the series does introduce several new features to the Pokemon Universe (namely online battling and trading), and the storyline at least attempts to be epic. But the selection of Pokemon available to the trainer is relatively limited unless they're willing to put in a lot of extra effort in not only this game and the ones preceding, but other non-traditional Pokemon Games.

The bulk of the Pokemon encountered in tall grass consist of perhaps a handful of common Pokemon that become extremely annoying (Starly and Geodude are probably the most notable.)
And encountering other pokemon in-game practically requires a schedule to remember what pokemon are available when, and in what zone.
My biggest disappointment is that a lot of Pokemon can only be obtained AFTER beating the Elite Four, by swarm, GBA cartridge transfer, or GBA cartridge insertion. You essentially have to act as a Pokemon Breeder to get Pokemon to learn certain moves, as well.

It's simply too much of a headache to bother with trying to get any of your favorite pokemon in Diamond and Pearl without Heart Gold/Soul Silver. It often takes too much time, too many other games, and too much breeding to be worth it.Get more detail about Pokemon - Diamond Version.