That probably, statistically, explains why I have only encountered poor Mercure hotels. I can't say I have had any "bad" ibis stays, though, although I couldn't sleep at all in the one in central Milan. I just don't like the ibis chain or the feel of it. Give me Holiday Inn Express any day.
I am now getting tempted to try this Mercure in Madrid on my next visit. I found the review by Goldorak very interesting to read, despite what I wrote.