Kind of Hard.
The game gets harder each time you progress.
Also, about the bosses:
Team Meanies (Gengar, Medicham and Ekans) are pretty easy.
The Legendary Birds are hard, they will be harder depending on the Pokémon you started.
If you're playing as a Grass starter, you will be demolished by Articuno and Moltres. (It's a bad start for you m8)
If you're playing as a Fire starter, Everything is Neutral against the Fire starter you started off, except Moltres because Fire resists Ice.
If you're playing as a Water starter, then Zapdos will demolish you up.
Also your partner should be a Mudkip, because it has a good base Attack stat early on.