I think Lou was playing the character of herself, kind of like what Paul Chowdhry does but on a much more basic level. Aisling I don't particularly dislike and I'm not sure why she gets any hate as I didn't think she was stand out annoying, but she definitely is more just being herself.
I guess it's a similar reason to why any celebrity is disliked by some and liked by others? It's all subjective, and what appeals to some is an anathema to others.
People like Michael McIntyre, Jonathan Ross, Jimmy Carr, Iain Stirling get plenty of dislikes as well as likes. I'm not sure why some seem puzzled that the same might just as validly apply to the likes of Aisling Bea or Desiree Burch?
As regards Lou, yeah, I think you're right that she's always 'on' and playing a character. The trouble is, it's a loud, in your face character that demands attention so while some may absolutely love it, if you don't then it quickly becomes very annoying. I'd say she's OK in small doses, and I found her OK for a few episodes, and for the first couple of days on House of Games. But by the end of both I'd seen more than enough of the act and was finding her very hard work.