Hmm lets see here, these are the sets I was around for:
Fallen Empires: much maligned because of lousy commons structure (4 Thallids - gotta catch `em all!) but actually a power set for tourneys because of how much it helped weenie decks.
Ice Age: Mixed bag. Most of it was junk, but then occasionally you`d pull a gift like Stormbind or Jokulhaups. And of course the painlands were seen here first.
Homelands: Oh...My...God! They actually succeeded in printing a set without a single good card - okay, Autumn Willow made the grade, and Serrated Arrows got used. But this set stunk.
Alliances: A very popular set at the time, and even in retrospect it makes a good impression. Good, but too slow to be fun to play with.
Mirage: Poor. Probably justified in being compared to Masques - slow and balanced (AKA dull and boring). Hammer says otherwise.
Visions: WooHoo! Now we are talking! Fireblast! Impulse! Vampiric Tutor! Sewer Rats! Tithe! Squandered Resources! Frenetic Efreet!
This set was incredible - simply the inclusion of Fireblast changed the game immeasurably. The art was suspect - a bit soulless if you ask me - but by golly the cards were a revelation.
Weatherlight: A fun set - perhaps the first to really satisfyingly follow through a design theme and make a coherent whole. Contains a mixture of powerful cards like Firestorm, Ophidian and Gaea`s Blessing but notice how few vanilla cards there were, which made it superb in sealed - the first modern expansion IMHO and a very strong contender for best set.
Tempest: Shadow! Hoo-boy, was shadow some good for tournaments - a total kick up the ass for beatdown decks. Buyback - the best ability EVER! Definitely a contender for best set - Living Death, Tradewind Rider, Whispers, Humility, Soltari - something for everybody.
Stronghold: Slivers + Spikes - woah! Wall of Blossoms as well. Another top notch set that gave something to everybody. Unfortunately outshadowed by the next set...
Exodus: A personal favorite because of the inclusion of so many of my all time favorite cards. Survival, Recurring Nightmare, Spike Weaver, Spellshock... but its the RecSur combo that clinches it for me - 5cDeath was for 18 months the best and most enjoyable deck to play thanks to these two cards. There is very little junk in Exodus, but I think it needs to be seen alongside it`s Rath Cycle brothers.
In my opinion Rath Block is THE PERFECT magic environment - perfectly balanced in every single way and I could play it for ever.
Urza`s Saga: A much maligned set, but on balance it did okay I guess. Problem was we spent so long clearing up the various problems with Academy and Time Spiral that by the time we had them finsihed it was just about time for...
Urza`s Legacy: And Memory Jar. Joy. Legacy is a superb set because it reintroduced the staple ability of 187 effects to T2 magic. That alone means I can forgive it for Memory Jar. Oh, I nearly forgot Rancor.
Urza`s Destiny: WOW! The power bar just goes off the scale! Almost every deck currently played in T2 is based around Destiny cards - Masticore, Keg, Treachery, Rector, Bargain, Negator... This is the set that defines T2 right now, because it is the set that has Masticore in.
Mercadian Masques: After Destiny it was always going to be a disappointment, but Masques has done alright for itself on balance. Pretty good set.
Nemesis: Hmm, maybe it will grow on me. It certainly has few cards that break the curve of power cards, but a nice number are bubbling under so it`s probably a little early to say.
2. Urza`s Destiny
Notice a trend? I hold that the last set of each block always has better cards than the earlier expansions and I was right to predict that when Destiny arrived. I`m willing to put money, right here right now, on Prophecy being an extremely good set - bringing whole new decktypes to the environment in time for Urza`s block to rotate out.