Tried this tonight with a buddy. Even with my lower power cube, it feels like insanely powerful magic. I can confirm that this format absolutely eliminates the number of non-games that happen. I also agree that the format definitely warps the power of certain cards, but honestly I don't really think that is a bad thing. It allows you to experience your cube cards in a new light by turning some of them on their heads.
We ended up only playing 2 matches. I almost wonder if doing best out of three match wins (with best out of three game wins within each) is a better way to go. 4 Match wins is a lot if you go 2-1 in every game and 4-3 on matches. 21 games plus deckbuilding?
Also, we felt a bit weird about being able to get graveyards back but not exiled cards. In particular, it makes flashback cards kinda shitty. We experimented with a 4 life penalty for shuffling RFG'd cards back into your deck (because we agreed that exiled cards should always be harder to get back than graveyard cards). I can say that it really hurt to pay the four life, but I did do it once. I guess an alternative rule would be a life penalty to put the exiled cards back into the graveyard, but I'm not sure that really works as intended; I'd rather that people couldn't tutor a collection of flashback cards back to their graveyard for even 3 life.
I think I might actually like this even more than grid draft, but maybe that is just because it is fresh. I really like the lands. We actually didn't end up putting them in our decks, but just the fact that I had to consider, and decide not to use the lifegain land enriched the experience. (I was playing burn for most of the games)