How I rank the seasons:
1: I was very impressed with this season. I was a fan of the '90s Flash series, but this first season just took the ball and ran with it. Particularly liked the twist with Harrison Wells. And they did a great job casting both Reverse Flashes.
2: A strong season, with another great villain (even though looking back they used the same twist). I still recall when Zoom beat the snot out of Flash, that was an edge of your seat moment. Also enjoyed Tony Todd voicing Zoom.
4: I was burned out, or rather bummed out by Season 3, so it took me years to finally look at this season, and it turned out much better than I thought it would be. The Thinker was a good non-speedster villain, something the series sorely needed.
5: I also liked this one, though I felt they had Nora acting too young for her age. When I had seen Klein on there when the season was actually on, I just couldn't get into his performance. But after looking at it all the way through, I thought what he did was affecting enough.
7: I looked at a lot of the last seasons out of order, but from what I recall, I did enjoy this season well enough, though I felt Godspeed was given short shrift, despite casting an actor that looked like he came right off the comic page. And his Godspeed suit looked great.
8: I thought this season started strong with "Armageddon" though it didn't stick the landing. However, I thought the final arc wasn't that good, and the suit they had the big bad in looked horrible.
9: Similar to the eighth season, I liked how this one started, though for a final season, I think they could've made better use of the middle episodes, and while I appreciated Eddie coming back, I didn't like what they did with him. The costume design also left a lot to be desired.
6: If I had seen this one when it actually came out, I'm sure I would rank it higher. But seeing it years after Infinite Earths, plus succeeding Flash seasons, I found all the foreboding about Barry's fate tedious. I did like Bloodwork though. He reminded me of Venom.
3: This was a season that started promising, but once I learned who Savitar was, that was it for me. I just didn't think he was a convincing enough villain, outside the suit. Kudos to Tobin Bell for voicing him though.