Firaxians would cry their way to the bank at the suggestion that Civ5 was a failure, and to be honest it's fairly dubious to claim that the community seems overall rather critical, as opposed to saying that it seemed overall rather critical. The expansion packs have drastically changed the general consensus towards the game. Sure, there are people who still aren't fans, but it's quite a minority, and the same can be said about every iteration in the series. Firaxis would certainly not be seeing the game as a failure or as full of huge errors, even though they obviously would be willing to recognise some deficiencies (as they did following Civ4, which is essentially what big design changes like 1upt are a response to). Very many people would say that Civ5 with BNW is the best civ game ever, and even those who disagree would for the most part recognise it as good game, even if trumped by Civ4, Civ3, Civ2 or Civ1, depending on preference.
The combination of XCOM and Civ5 mean that Firaxis has been hugely successful with its major strategy projects, so I imagine it would be unlikely to move away from that. However, a new Civ straight-away is certainly no guarantee if they're continuing to be ambitious.
@plastiqe - the public beta is something they haven't done before, but it's very incorrect to say they've mostly kept to themselves, given how much interaction they have with the community in general, and how prominently they have used the Frankenstein team. The fact that Jon Shafer was a community member surely shows this.