Without wanting the to turn the thread in to a moanfest, when folk pay their money in, they're entitled to their opinion on matters whether it's positive or negative irrespective of whether or not someone is doing something for free or not. For what it's worth I'll endeavour to be constructive when I feel the need to criticise.
From what I've listened to previously, the singers for me aren't to my taste. Generally I prefer singers who don't over sing songs. Also there are certain songs that just shouldn't be covered or messed with, not through lack of effort or talent, just because the originals are just that good, anything by Alisha Keys for example. Let's be honest there's no right or wrong when it comes to musical taste, one man's idea of a classic is another's idea of a horrible racket.
I certainly admire their effort though, I couldn't do it. The singing gene didn't get passed down from my Welsh Dad to me.