This is the shake up that the Pokemon games have needed for years. Is it perfect? No, there is definately areas of improvement and I hope they continue to build upon this formula.
Arceus doesn't do anything new as an rpg, however, what it does it does well, and everything flows so smoothly in the game that is a blast to explore and play until the very end.
Switching between exploration to battle is seamless, going from walking to riding to flying is a snap. Having the option to fight or be stealthy to catch pokemons is very freeing and let's you approach the game like you want. Battles are much faster than in the main series. The downside is that there is less room for strategizing or setting up, but it keeps the flow of the game
The pokemons have different sizes, and we can finally see them relative to each other. Seeing a giant steelix fight my little pullip is an imagine I will always remember. Their attacks are better animated and actually looks like they are battling each other. It finally brings Pokemon to live in a way that no other game in the franchise has done. The difficulty of the game feels perfect, not too hard and not too easy. I hope they continue to keep this balance as the pokemon games tend to suffer for being too easy.
The story is probably the weakest part, and the start of the game does take about 1 hour or so to actually get going. The game would benefit from getting some voice acting and having some really cool cutscenes showing off the pokemons. The action adventure aspects of the game are very minimal (i.e dodging) and I do hope they expand on it. It is an interesting gimmick but not game changing.
The side quests, called requests in this game, are pretty monotonous and not particularly fun for the most part, however they add to the atmosphere of this world filled with strange creatures called Pokemon and how the villagers learn about them and start living with them. However, a lot of quests are simply completed by you just going on the world and doing regular stuff. And this applies to a lot of the gameplay loop, your goal is to catch Pokemon and by catching Pokemon you gain all sorts of rewards, money, reputation, quests, items, etc... So going out and catching pokemons at every chance you can feels extremely rewarding
All in all, I spent 46 hours on the game, catching all the pokemons and finishing the story plus some side quests and the game was a joy to play every step of the way.
I definitely recommend this game for any Pokemon fan, however do not expect this to be breath of the wild, it is a much casual experience but it is a very fun one.