Chancellor of the Annex was pretty underwhelming to Standard players back in 2011. Of course it was. The ability to prevent your opponent's one drop was cute, but when were you going to get 7 mana to drop her onto the board? Then, making your opponent's spells essentially cost one more mana was more annoying than anything else.
Here's the thing. Legacy found a home for her... in Reanimator decks! Having her in your opening hand is pretty good in that format, as shutting down a turn one spell is a lot more important. Then, with all the ways you can discard the Chancellor into your graveyard, you'll easily be able to bring her back later. A 5/6 flyer is really tough to deal with, and since the spells in Legacy are so much more powerful than in Standard, keeping your opponent one mana off from potentially "going off" can win you the game while you bash in with this Angel.
The Chancellor cycle was pretty cool to play with in draft with New Phyrexia. Chancellor of the Tangle was the best for Standard play, but Annex is probably the best of them in the long-run. She was bulk forever, but now people realize, she's pretty good. And in Commander, since she affects each opponent, she is really, really annoying. Great card, and you should own at least one if you play any kind of Reanimator strategy.