Gen 4 had a lot of issues.
>way too much fucking blue and purple across the dex, seriously look how many Pokemon are either blue or purple, it's uncanny.
>a large portion of the pokedex was unobtainable during normal ingame playthroughs, tons of gimmicks to get them like honey trees, underground, great marsh, etc
>brought back baby Pokemon for mons that didn't need it
>like 20% of the dex is cross gen evolutions that are still debated to this day like Magmortar or Ryhperior, only like 2 of them get by without much heat
>is the generation that started cranking the fuck out of the amount of legendaries, I think double the amount Gen 3 had
I also think it had a weak dex overall, tons of shitters like Cheerim, Purugly, Lumineon, fucking Chingling, etc.
I really have to wonder how this generation would be remembered if an absurd amount of people didn't start playing Pokemon with them, the reaction to BDSP makes me think that without nostalgia, Sinnoh is very low tier.