Except for original Ravnica and Time Spiral, every one of the 20+ three-set blocks has been (approximately) two reasonable sets that were on theme and made sense, plus one totally pointless one that everyone hates.
I'll only rate full blocks that were new whilst I was playing (I started with Dissension):
Time Spiral (second set I after I'd started playing): "Welcome to MTG, he's a crash course of the last 10+ years you missed" - Awesome, researching the references was fun
Planar Chaos: Kind of confusing but a lot of really cool individual cards (I still remember that Damnation preview)
Future Sight: Top 5 Set of all time. Just fucking......WOW
Lorwyn: Top 5 Set of all Time - excellent draft format, Merfolk da best
Morningtide: Thanks for making the limited format worse? Class tribal, Bitterblossom and Mutavualt were cool though
Shadowmoor: Only format where sealed is more fun that draft. Meh
Eventide: Figure of Destiny is sweet. Otherwise shrug
Shards of Alara: OMG why is everything terrible and vanilla? (NWO didn't have a name yet but it got introduced here)
Conflux: Oh hey limited is actually playable now <3
Alara Reborn: Lots of powerful cards, cool gimmick though it was clear it was stretched thin
Zendikar: So many powerful cards, too bad limited is shit :/
Worldwake: Limited is still kind of shit but less so? Powerful cards are cool though
Rise of the Eldrazi: Top 5 Set of all time, best retail draft format ever. My only regret is that I didn't get to draft it even more
Scars of Mirrodin: Kind of neat. Much better even at a glance than old Mirrodin. Not a fan of what Poison did to limited.
Mirrodin Besieged: A fine set. No strong feelings.
New Phyrexia: Top 5 Set of all time, AMAZING cards, poison is ok in limited now
Innistrad: Top 5 Set of all time. Excellent limited format
Dark Ascension: Like Innistrad but much worse in every way. Thanks for making limited worse?
Avacyn Restored: A few cool/powerful cards but limited was TRASH. Garbage set overall
Return to Ravnica: Amazing cards all over the place, decently fun limited format. Great set just outside Top 5.
Gatecrash: Talk about a Crash and Burn
Dragon's Maze: What was even the point? Trash cards everywhere. Fuck off with the Cluestones too.
Theros: Great cards, decent limited format
Born of the Gods: Irredeemable trash
Journey into Nyx: Why are we just NOW getting Constellation?
Khans of Tarkir: Great cards, great limited format
Fate Reforged: Thanks for making limited worse? Some sweet cards though
Dragons of Tarkir: Good cards, mediocre limited format
I have gone back and researched/played with older formats but again the perspective will be different looking at them historically rather than in the moment.