I've been somewhat enjoying a relatively faithful return to gen 4 but there are some key things missing from the originals and a few missed opportunities. I'm about halfway through the main story now but I'll update if anything changes my opinions.
The secret bases appear to have been completely gutted, you can't customize them with furniture and traps anymore it's just the statues and they don't even look very good. There is no capture the flag anymore either. This was one of the things I liked the most about the original games and they just completely removed it for seemingly no reason. You could have had statues, chairs, mats, tvs, tables, plants, plush dolls etc. why is it just statues? Big whiff there.
Also the exp share is forced on you in this game, it wouldn't be soo bad if they adjusted the enemy trainer levels to make up for this but instead they chose to use the regular diamond and pearl levels for battles and because of this my team has been an avg of 6-10 levels higher than everyone i fight, even rivals and gym leaders.
The biggest missed opportunities for updates/changes in this game are:
1) not having the ability to change the camera angle up and down like you can in animal crossing, I found myself passively trying to do it through the first few hrs of gameplay.
2) having a more cohesive art style, the chibi overworld design isn't necessary anymore. let's go pikachu and eevee look much better by comparison.