They used to be excellent. I stopped buying them a couple of years ago because I thought they'd gone off the boil, and switched to Primark. M&S swore they hasn't changed supplier or anything.
The biggest downside with the Primark tights though is that they wear really quickly at the top of the thighs.
Anyway I bought some M&S tights yesterday thinking they must have gotten better again. NO! They are AWFUL. No stretch. No flex. Short in the body (I'm 5'6"). Just awful.
I'm a bit of a fatty so really struggle to find good XL tights. M&S; please make your tights good again!