The Sinnoh games were the first for the DS system and made a lot of the overhauls that improved the game.
The split between physical and special moves for every type.
Wireless communication.
Widespread access to entry hazards thanks to Stealth Rocks.
Evolutions and pre-evolutions for a fair number of Pokemon.
The Battle Frontier.
Easy access to what's become the OU tier in competitive. A large chunk of the Pokemon in Sinnoh are viable in battling. So many fantastic pokes are on every route.
The downsides were I believe a really slow ticking down of enemy health bars and increased difficulty in opposing trainers.
Also very few Fire-types before the National Dex.
Those are among the many reasons people are divided over the remakes. Gen 4 was the first iteration of the game where anyone with internet access could play with others.
My take is the lighting effects for the in battle sprites needs an overhaul, but the rest is fine. Don't care if it's chibi, the old games were too. Give us more Megas and hopefully a national dex again.
My favorites are still Unova, but so far Sinnoh has had the largest impact on the games as a whole. Hopefully they keep the games closer to Platinum. It just had more everything than DP.
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