The mode is a triumph over adversity idea wherein you'll pick the five heroes the opposing team has to play and they'll do the same to you. It's about being the best at either screwing other people over at the drafting phase or at making your own terrible team compositions work. Or both.
The mechanics of how it works are as follows:
- You're playing 5v5 on Summoner's Rift.
- Each player on your side gets to pick a champion for the enemy team.
- Bans still exist so you can get rid of champions you really don't want to get stuck with or that you don't trust a teammate not to give to the opponents.
- The champions you can pick from are your team's collective pool (I think that means you can give them anything your team has access to play, be it free rotation or purchased).
- You can play any champion of the five you're given regardless of whether you have it on free rotation or purchased access.
Thing is, I can see that some people would be interested in taking on the game part of the mode as a real challenge but, having played various game modes for MOBAs, I'd say the interest here is generally in the drafting phase and that interest wanes when you get into the game, particularly if a player ends up with something they simply can't or don't want to play.
Probing through the comments section, it seems like dodgers (players who then abandon the match) are a big problem judging by the feedback. Riot is aware of this and has spoken about some methods to discourage dodgers for when the mode leaves the PBE. They include dodge penalties of up to two hours and a reward icon for non-dodgers. Another is players trolling their own team by giving the enemy a strong champion.
From the feedback and my own experience of various game modes I'd say it'll get a flurry of attention when it's first out but then settle down into a relatively low number of players, some looking for a personal challenge, some wanting to let off steam with a muck-about mode and some just trying it out.
It'll be interesting to see whether it ends up being fun or more of a thought exercise with a hugely wonky and potentially horrendous trip to Summoner's Rift at the end.
If you fancy wading in the mode is live on the PBE - you can find info on how to access that here.