Return to Ravnica block limited is some of the most fun I've had playing limited. Each guild has lots of little nuances, synergies, strategies. Each guild has lots of ways to play, and cards that interact favorably not only with their own guild, but a bunch of other guilds as well.
I've played a lot of Gatecrash lately, so I'll highlite some nice interactions I've noticed.
Agoraphobia - A nice little card that's well worth the price because it renders a creature completely worthless as anything other than a blocker. But it has a few other nice tricks. It is an extort enabler. Becuase it can bounce itself, you can use it and an extort outlet to bleed your opponent out of a stalemate. It is also an evolve enabler. Stick it on one of your better evolve guys and let it get buffed up from a few other critters. Once it's sufficiently big enough, bounce the aura and go to town with your newly biggified beastie.
Gatecrash has tons of evasive things at lower rarities, things such as Way of the Thief. Now, I played a good deal of M13 limited, and let me tell you Tricks of the Trade was always a beating. Well worth it just for how badly it would screw up your opponent's calculations of your game clock. This does that, but even worse. How scary is an unblockable dude when you're in Bloodrush colors, or once you've stuck a cipher spell or two on it? Plenty.
Act of Treason - Clears a blocker, and gives you a third trooper for your Battalion battle plan.
Alpha Authority is in the same limited environment as Ripclaw Predator and Madcap Skills. Just sayin'
Encoded spells become cast, so you can extort off of them.
There's just so much to do, and there will be even more in Dragon's Maze when the guilds cross streams, so to speak.
Scavenging onto Dimir's multiple unblockable critters. Detaining blockers away for an enormous Bloodrush beating or another cipher trigger. Blistercoil Weird getting a free untap from those cipher triggers. Moving counters off of your Simic Fluxmage onto your opponent's Unleash dude.
I can't wait.
What's the coolest experience you've had so far playing Return to Ravnica or Gatecrash limited?