6th Gen is where is all starting going down hill for me. Megas were a great concept, but they never built on them. 6th Gen also had one of the more mediocre stories with Team Flare and the Champion; I actually liked the Looker Story better. Plus, Zygarde was just an after thought.
7th Gen had a great twist with the real bad guys, a nice shake up with trials instead of gyms, and a key girl character that was missing in both the 5th and 6th Gen, buy it was lacking basically everywhere else. No good rival, no real antagonist group. Another great Looker story.
8th Gen probably worst thus far as Sw/Sh had only a few good things. Nice twist with Eternatus Ending instead of Cover Legend, but no antagonist group whatsoever. Whenever Rose would cause trouble, Lion literally took care of it. What was the point? Pooh rival. Pooh climate story that had no relevance until the very end. And poor flow to the game. You literally have no gym battles for hours, but then it is almost a rapid fire. Dynamax was nice, but I feel it took over the games themselves.
Arceus has made everything since 5th Gen look so average and without true thought. Different, but very fun.