First entry of the PMD series starts of fairly strong, but heavily depends on the Pokemon you choose at the beginning. Many of the main story dungeons & bosses can be very unforgiving depending on the Pokemon you choose, and unless you want to rely on RNG you'll use a wondermail generator to insert items & TM's into the game to help you out. Thankfully these games are a bit more forgiving when it comes to stats & matchups compared to the mainseries; you can improve & tweak your Pokemon with: Gummi's, linked moves, and stats can be boosted much further than in the mainseries titles. (Being able to put the map on the top screen immediatley ranks it above Red Rescue Team)

Massive visual improvment over Gen's 1 & 2, GBA really felt like you had SNES quality games on the go. Unfortunatley many Pokemon are still useless due to the lack of physical/special split, and this probably has the weakest postgame in the series till this day. Improves somewhat over Ruby & Sapphire in terms of content, the postgame is still very weak but not quite as much. I would give points for the Battle Frontier but no one in their right mind is making a competitive team without cheats, and even then the AI can still cheese the hell out of you. Priotitizes "top tier" Pokemon within archaic combat mechanics by todays Pokemon standards. Overall Hoenn is still a great region with many memorable locations & Pokemon, plus the legendary Gen 3 trumpets leading the awesome soundtrack.

(Good luck if you pick Treeko)

This is what Diamond & Pearl should've been to begin with. Gen 3's engine still has better performance overall, but Gen 4 is no longer molasses when it comes to it's speed. The Pokedex is a massive improvment and all of the new Pokemon are available during the main story. The Physical/Special split can now be fully realized with previously gimped Pokemon now able to take full advantage of their assets. Single use TM's are still a real pain, and make attempts to build a competitive team for online and the Battle Frontier that much more brain numbing. Sinnoh is arbuably one of the best regions in Pokemon, loaded with charm & personality from the incredible soundtrack & environmental storytelling. Like with Emerald this feels like the complete story compared to Ruby/Sapphire & Diamond/Pearl; Platinum really does Sinnoh & Gen 4 overall justice, and is a top-tier Pokemon experience.

Do not bother with Diamond & Pearl, just play Platinum. The game engine is atrociously slow, especially during battles & surfing. The Physical/Special split is not enough to save this game, especially when most of the new Pokemon are locked to postgame which in itself is also bland. We excused the flaws back in the day when this game dropped since it's all we had at the time, but in hindsight the flaws are simply inexcusable. This is the one Pokemon game that feels like a beta version rather than an actual product ready for release to the masses.