Khans is a badass set (getting a bit long in the tooth) but better than Zendikar? I wasn't really around for those days, but isn't Zendikar one of the most beloved sets of all time? Or is that just cause of Emrakul?
I saw a partial poll on this once, although I can't track it down. If you break it down, there's really about five categories for blocks: sublime (Ravnica and Innistrad), good (Invasion, Mirrodin), middling (Alara, Shadowmoor, Theros), marginal (Lorwyn, Odyssey), and bad (Masques, Kamigawa.)
Zendikar is probably pretty firmly in the "good" category; had a bunch of popular strong cards, did some interesting stuff in Standard, and has a bunch of cards that are cross-format staples years later, plus had popular gimmicks like the full-art lands and the "Hidden Treasures." (The big downside is that ZZZ was a seriously mediocre draft environment.)
Given the reaction to date, Khans is probably hovering somewhere between good and sublime. It met a popular fan request, it's driving a Standard environment that people are super happy with after suffering through Theros, it's got a ton of useful and interesting cards that are usable across multiple formats, and it's considered to be quite high on the list of all-time draft formats. Add the fetchlands and it could definitely hit the top category in a few years.
For as much as I hate watching Siege Rhino games, I love watching Whip of Erebos games. I love that card so much; it's by far my favorite thing to come from Theros block.
I stayed up until like four AM watching the Magic World Cup finals and I loved watching the Whip matches -- so much weird, complicated stuff could happen and there were so many interesting shifts in board control. (It helped to have someone as good as Turtenwald playing in the matches, too.)
And with the black wrath being modal, yep. Cycle.
Two cycles or a broader set theme, even; the black wrath is a rare and this is uncommon.
Hmm, is it possible that Dragons of Tarkir will have a way to apply entwine to other spells?
... Probably not.
A legendary artifact that does this is a card design they've probably had sitting in their back pocket for years. If they're ever gonna do it, this would probably be the place.