Naturally most people who saw the show liked it because they were mainly soap fans who were only there because she was in it. Apparently she had huge problems talking posh when it was required, sounding no different to the Eliza Doolittle Higgins first discovers (rather like her pitiful attempt and failure to do a posh accent when playing an ex pupil of an exclusive private school in her now infamous pre opening credits appearance in Midsomer).
With regard to the Olivier Award, this was more in recognition of the commercial success of the show rather than any talent demonstrated by La McCutcheon. Jonathan Pryce's look of disgust and dismay when she won the award is more typical of the views held by genuine theatre folk.
Well, that may be so. I didn't see the show myself, so can't really comment, though I think Pryce has made it reasonably plain that his reaction was down to his frustrations with her absence rather than her performance.