I've played since set 1 so here's my definitive ranking of the sets thus far (set 11)
1. Gizmos & Gadgets (Set 6) [Master]
2. Fates (Set 4) [Diamond IV]
3. Dragonlands (Set 7) [Master]
4. Festival of Beasts (Set 4.5) [Master]
5. Galaxies (Set 3) [Diamond IV]
6. Return to the Stars (Set 3.5) [Diamond IV]
7. Monsters Attack! (Set 8) [Diamond II]
8. Glitched Out! (Set 8.5) [Master]
9. Inkborn Fables (Set 11) [TBD]
10. Neon Nights (Set 6.5) [Diamond II]
11. Beta Set (Set 1) [Platinum I]
12. Remix Rumble (Set 10) [Master]
13. Dawn of Heroes (Set 5.5) [Master]
14. Horizonbound (Set 9.5) [Master]
15. Uncharted Realms (Set 7.5)
16. Reforged (Set 9) [Diamond III]
17. Reckoning (Set 5) [Diamond IV]
18. Rise of the Elements (Set 2) [Platinum III]

1-13 my average enjoyment is probably about a 8.5/10
14-18 it's probably about a 4/10

My rank for each set more or less correlates to my enjoyment of the set. Higher rank = more enjoyable