I'll write up more at some point but here's a longer look at Kami/Rav:
Kamigawa Block was already one of the most interesting and varied formats in a long time, and the great mana and gold cards that Ravnica brought spiced it up even more. After Ravnica's release all of its guilds were represented at the highest levels of play: among the baseline decks were WR Aggro, BG Aggro or Midrange (based around Dredge to some degree), WG Glare, and Ub Jushi Blue (one of the initial 'draw-go for the early-/mid-game, then tap out for threats' decks - in this case, Meloku/Keiga). The Ravnica shocklands + Karoos along with painlands meant you could easily play 3 colours in certain combinations, and people made the most of it. The Gifts decks that dominated early Kamigawa block became retooled with better mana and lots of new toys; the card Gifts Ungiven ended up in shells ranging from draw-go control to Greater Good combo to Wildfire-Loam. One of the coolest, if overrated, decks was Fungus Fire, a WRG Control deck with Sunforger + Vitu-Ghazi providing inevitability even against control and a ton of removal to keep up with aggro.
Here's a good summary of the format going into Worlds.
Worlds itself shook up the format a fair amount. The Japanese Ghazi-Glare deck with two different transformative SB plans - Greater Good + Yosei, and Congregation at Dawn into hate/Hierarchs, which often came together in the same post-SB configuration to let you chain Yoseis - dominated the tournament, but there with some combo innovations too with Frank Karsten's Greater Gifts deck and Akira Asahara (probably the most well-known wacky deckbuilder from the 2000s) playing Enduring Ideal.
Guildpact arrived for the first full Standard Pro Tour in forever and had a massive impact. Stomping Ground by itself gave Kird Ape and friends a point of entry into the format, and Izzet and Orzhov both had a wide range of decks under their banner. Wafo-Tapa surprised nobody by playing
UR Control, the South African Tron deck from Worlds gained a viable manabase and Izzet Signet and become great, and two different obnoxious griefer decks - UR Magnivore, aiming to Boomerang/Eye of Nowhere/Stone Rain your lands, Time Walk with Remand, refill with Tidings/Compulsive Research, and close the game with Wildfire and/or giant
Magnivores, and Owling Mine, which used those bounce effects along with Exhaustion to stall while breaking the symmetry on Howling Mine/Kami of the Crescent Moon with
Sudden Impact/
Ebony Owl Netsuke. Meanwhile, with glacially slow BW Control off in its own corner, most worshippers at the Godless Shrine played BW Aggro which itself was heavily customizable - you saw the basic
Hand in
Hand deck mutate into Ghost Dad, which used the bevy of Spirits already in the deck along with blowout machine Shining Shoal to turn Tallowisp into an engine, and Ghost Husk, an Aristocrats forerunner based around Nantuko Husk +
Promise of Bunrei (the sac effects being notably great in the Umezawa's Jitte fights that happened in every aggro mirror) . The
namesake Ghost has really awkward mana requirements for Cube but was fantastic in this format.
Along with introducing their own set of two-colour decks based on their guilds, each set in Ravnica block gradually opened up design space for three-colour decks. This created a really interesting effect over time - though it was frustrating for Rakdos fans that they had to wait an extra 6-8 months to play their favourite deck, you had a guaranteed change in the format in parallel with more speculative changes. Guildpact was no exception - Naya Zoo was the most popular deck
at the PT but Abzan Control was also a hit. A personal favourite to come out of that tournament was the
UWR Firemane deck, which had plentiful lifegain and removal against aggro and Firemane inevitability to lock out control plus
Zur's Weirding to steal games. Also in the Top 8 without a single dual land, by necessity, was
Heartbeat Combo which may have been the best deck the whole time (and which also could transform into a ramp-into-Legends deck with tutorable sweepers/Jitte via Muddle the Mixture).
Around this time came the return of a beloved 'sub-format': Team Unified Constructed PTQs/GPs. The rules were different - nowadays you can only play a card in one deck, back then your combined decks had to be a legal deck - and they forced players to explore the boundaries of the format. You can have a Steam Vents deck, a Godless Shrine deck, and something else - but if every team does that, some Steam Vents decks are better than others in the 'mirror', ditto for Godless Shrine decks, so do you pick your third deck with that in mind or do you sidestep that problem entirely? Heartbeat didn't demand any shocklands but did need Remand, which was a problem for UR fans, and so on. Decks that had died down, such as GW, reappeared to attack from a new angle.
Dissension shook the format up again ahead of Regionals. UW saw the same split as BW and UR had, with aggressive decks on one hand (WW with a light blue splash or WU fliers headlined by
Pride of the Clouds) and classic UW Control (our Nationals was won by UW splashing Vitu-Ghazi and Loxodon Hierarch). UG Aggro-Control existed back around Worlds but now got a shot in the arm. Rakdos fans finally got what they wanted as BR Aggro quickly became a deck to beat. Three-colour decks continued to flourish: UWR now got the missing dual lands and some extra tools, the Glare decks poppued up again with new Chord of Calling targets or a
Supply // Demand toolbox (and even
Dovescape!). Tron decks and the remaining few non-blue control players splashed for
Simic Sky Swallower. With great mana and tempting rewards for pursuing any colour combination, you could basically do what you wanted.
Two decks rose to prominence in that era.
Sea Stompy, a URG aggro-control deck, married the fast pressure of the old RG Aggro decks with the disruption and tricky creatures offered by UG and Thoughts of Ruin as a pseudo-Armageddon (or, if you were more discriminatory,
this list with 4 MD Stone Rain and 4 MD (!) Cryoclasm) .
Solar Flare grafted a reanimation subtheme onto an Esper midrange deck but the real innovation was the Signets + bouncelands + 3-drop (Compulsive Research/Court Hussar here) shell that defined midrange/control in Ravnica Block Constructed and later Ravnica-Time Spiral Standard. Somewhere in here
Snakes (?!) started running over MTGO though they never made it to the paper plane.
That wasn't the end of the story. Nobody was quite sure why Coldsnap existed but it did, and it was billed as the third set of the Ice Age block - and it seemed to reflect some of that mid-90s design philosophy. Counterbalance + Sensei's Divining Top was unleashed on Magic for the first time as a Standard deck,
winning Japanese Nationals. Mishra's Bauble let a Ninjas deck with
Erayo, Soratami Ascendant burst onto the scene. In a perfect bookend, future GOAT Paulo Vitor Damo da Rosa won his Nationals with a revived Enduring Ideal deck by Akira Asahara featuring Counterbalance-Top and a snow engine featuring Scrying Sheets,
which he called the best deck he ever played years ago.
...also there was
Battle of Wits
This isn't just pure nostalgia, as the format did have downsides: there are good reasons WotC don't let you bounce lands at 2 mana or blow them up at 3 mana any more. Creature mirrors often came down to who drew more Jittes, and Counterbalance-Top was as obnoxious as in every other format it was part of for its short stay. That said, there are few formats I could write in as much detail about or that even offer that level of detail at all.
