I'll just do a quick run down:
Kanto: 9 - Pretty much perfect, with a few exceptions like the handling of Ash's team.
Orange Islands: 8 - Consistently good, no big complaints.
Johto: 6.5 - Started off great, but the fillers in the middle brought it down.
Hoenn: 6 - Good story-wise, but it dragged on for a bit and I wasn't a fan of that.
Kanto Battle Frontier: 5.5 - A great idea that was badly executed.
Sinnoh: 7 - Character development galore for Ash's Pokemon, plus well-developed rivals and villains.
Unova: 3 - Terrible for a variety of reasons that I can't be bothered to list at the moment.