Got the new chain and sprockets installed... It's feels like this is how it should've been from the factory.
Turns out that my rear wheel bearings are a bit lose. Also I think the rubber things inside the wheel that the rear sprocket sits on seems a bit loose. So I'm guess that + bushings makes the weird feeling.
But then again this isn't really a race bike so maybe my expectations of it being tight are a bit too high...
Now that the drive train + gearing had been solved time to move to the suspension :-D