I agree with Gin on a great many of his points, and personally I enjoy the champions mechanic. Think about it this way:
Before, you put all of the best OS cards in your deck, spammed them onto the field, proverbially rolled your face across the keyboard, and won.
Now, you can make a bunch of different decks to maximize the different unique traits of the champions, STRATEGIC DIVERSITY, and actually think and therefore enjoy the game more (I maintain that mindlessly steamrolling is not as fun as a game well played).
If anything, I believe that the champion mechanic now makes champions more collectible, simply because you can now build decks around each of them instead of just having one deck that runs 3 copies of each alleged "top tier" champ and then doesn't have room for some of the quirkier ones (looking at you, Serennia and Kraos. I still don't get why people hate Kraos now). I mean, Serennia may not be all that collectible as a common card, but now you can actually build a deck around her instead of having this old "Angels get flying if I've been buffed to 10 health" Lil' Lil card that she used to be.
Before, decks that had a strong OS presence were extremely linear. Now, you can make choices when you deckbuild. Sure, it's not as easy as it used to be. Sure, some of the crazier things had their power toned down. But I think it's better now, now that you can have a Kraos deck, a Serennia deck (okay, that one's more of a Dugg deck), a Harahel deck, and so on.
On a side note, I prefer to think of the OS changes as being "lateral" as compared to "vertical" in nerf territory. Yes, Precautionary Measures no longer wins the game instantly if you didn't run into a Mass Death. No, I'm not sorry to see the change to it. Overall, I still think the Overseers are really powerful.
And yes, I'm still waiting on their faction quests.