To throw my tuppence in (not that it matters much), Tumble was ok but not spectacular. The set is a little too big and shallow for my liking, and whilst the lighting and graphics are ok, the casting is a mixed bag. With all due respect, Alex Jones is NOT a Saturday night entertainment host; she looks lost and has very little charisma. Judging panel is ok, but nothing too spectacular. Celebs are a decent bunch, but it's quite clear they are doing it for the money (on some shows, like Strictly for example, this is barely noticeable)
For those criticising the BBC and ITV for their entertainment slates, it's clear you know very little about commissioning. Entertainment is one of the hardest genres to get away on television. With dramas you have good scripts, with factual you have well researched topics, but with entertainment it is just a 'fun idea' that you want to make for telly. You need to test your format, pilot it (and develop it further if need be) and even then it might get dropped. Broadcasters will only give you so much money for development, but you have to pay quite a bit out of your own pocket too!
Tumble is a solid idea. As with all talent shows, casting (in every sense of the word) is important, but the execution is even more important! There is the potential for a huge hit in there, but they need to find out where they are going wrong themselves. Whilst first impressions always count, I normally give a show at least 3 episodes to settle. Then a serious judgment about recommissions can begin to be made.
The only certainty in entertainment telly; if the ratings climb, it will get a recomission!