It's the worst set they've released in a very, very, very long time.
Like, a REALLY long time.
Well, going back, trying to mediate personal feelings with abstract critical reception:
Khans of Tarkir is a fantastic set with a good followup and a bland last act, but at least one that affected Standard and had some decent stuff.
Theros is a set with solid design, great development, followed by a clunker middle and a solid final set.
RTR is a very good first set, a less exciting second large, and a total stinker final.
Innistrad is the best set ever, a perfunctory middle set, and the worst set of the modern era.
Scars of Mirrodin is a bland and slightly problematic set, a super perfunctory middle set, and the best last set since Future Sight.
Zendikar is two sets that are much more boring than people remember, and then the best draft set of all time.
Going through coresets backwards you get mixed-to-positive, reasonably positive, does M14 really exist I can't think of a single thing about it?, genius, tom lolpille, solid, neat.
...
Going backwards from today, I think the first set to really be clearly worse than BFZ is Dragon's Maze, which is basically just a complete and total failure of execution. To get a worse big set you have to bounce back to AVR, the worst set (by a big margin) in the time period we're discussing.
For context, everything in that window is still much better than true junkers like Homelands, Prophecy, or Saviors; probably all better than mediocre junk like Masques. Probably every large set besides AVR is better than Alara.
WoTC is really in love with their Ghirapur Gearcrafter / Sandsteppe Outcast effects.
Well, I mean, that mechanic is about 37% of all Hearthstone cards ever.
Homelands will always be second to Prophecy for me when it comes to bad design. The MTGSalvation Wiki lists that Prophecy had a "minor land sacrifice theme", which is inaccurate. It has a major land sacrifice theme, along with land discard themes, and "control no untapped lands" themes. I understand the set was made by people who hadn't made Magic sets before, but didn't any of them ever playtest with their cards and go "wow this is super not fun for anyone" at any stage in the design?
Yes, Prophecy is the worst set of all time, because Saviors is weak and shitty, Homelands is boring, weak and shitty, but Prophecy is boring, weak, shitty, and
insulting.
Not people who hadn't made sets before, though. Design team was Mike Elliot, Bill Rose, and Mark Rosewater (aka one of the most prolific designers ever, plus 2 of Magic's 4 current senior leadership.)