A Generation 4 discussion?
Generation 4 will always have a special place in my heart. When looking at its overall Pokemon, Sinnoh has my favorite Pokemon designs out of all the regions we had thus far, some of which are even my favorite Pokemon to this day (like Shaymin, Gallade, Luxray, Roserade, the Piplup line, Dusknoir, Darkrai, the Creation Trio, the Lake Guardians, I could go on and on).
Diamond and Pearl had some pretty big issues though, namely the slow battle speed and the fact some new Pokemon couldn't be caught until after you beat the game (the first time I learned that Gallade couldn't be caught until the post game made me pretty mad because I wanted one during my adventure). Then, you have issues such as the useless Defog HM, the really slow surfing speed, and then limited types because of how the main story Pokedex was handled. When Flint's team doesn't comprise of mostly Fire-types and only half of Volkner's team consist of Electric-types, you know there's a problem.
Thankfully, Platinum fixed much of these issues: better battle speed, surfing speed being vastly improved, expanding the Sinnoh dex to rightfully include those extra batch of new evolutions, and improving the type distribution in the Pokedex so that Gym Leaders/Elite Four members were using a full-team of their respective types.
But there are many other things I liked about generation 4. Personally, it has one of the most enjoyable postgames compared to the others (B2/W2 still tops it out though). The Underground was incredibly fun to use, to the point that shard and stone collecting was a blast to do; creating secret bases also made it fun, and if they brought back the Underground for the remakes, I can only imagine what a blast it would be if it could be used online. Even the Wifi Club was an enjoyable feature, namely for getting to play mini-games with people from around the world. The Battle Frontier was about as enjoyable as it was Emerald too. I also liked Team Galactic for reasons that Opossum already started. Oh yeah, did I mention it had a memorable soundtrack? Cynthia's battle theme, Cyrus's battle theme, Route 210 theme, Route 209 theme, Route 225 theme, the Mt. Coronet theme, Dialga/Palkia's theme, and Giratina's theme are among my favorite tracks that I can name off the top of my head. Oh yeah, and let's not forget we finally got the physical/special split and online play (though it was a bit limited at that time).
I even watched Chuggaaconroy's Let's Play of Platinum recently, and seeing the whole game again reaffirmed why Platinum is one of my favorite games of all time. You could say generation 4 is where my fondest Pokemon memories can be found.