Whatever it is, not all 2-can kits are immune. I'm certainly no expert, but I must have done over 30 kits (with a gap over the last decade, until February) and very few have tasted as good as commercial beer, even when conditioned for many weeks. However, the recent ones have been far better, which have comprised of some Brewferm kits, Woodforde's Wherrys, Coopers Original Stout and the Brewmaker Old English Ale. The latter is slightly young, but has far more of a twang to it than any of the others, despite a dry hop with some Challenger hops. I'd happily take my two identical tasting batches of dry-hopped Wherry over many, many, pub pints. I did add extra yeast in all cases but the Brewferm kits, as the tiny 6g sachets usually provided don't help.
It's only recently that I've begun to trust my methods enough to pass any judgement on the kit itself at all, with the help of this forum and a couple of other sources. Keep as many things consistent as you can.
I think the idea that table sugar in any quantity (at least cane sugar) adds a home brew taste is probably a myth. I've tasted a Belgian Tripel from one of the forum's all grain brewers that had over a kilo of cane sugar in 18L... and it was fantastic. It will certainly thin the body out, but I don't think cane sugar contributes to any off tastes as such. I think it's more likely that people tend to be using poorer practices generally at the early stages of brewing, a time when they are more likely to be buying cheap, one can kits to which bulk sugar is added. It's probably not the sugar's fault!
