I am intermittently a big fan of M&S, but at the moment nothing grabs. Too trendy or too frumpy.
My big whinge is classic smart black trousers. About 12/13 years ago I bought 2 pairs - different sorts - that were wool mix, elegant, well cut, reasonably priced, washed and didn't need ironing. I have worn them incessantly. Recently I tried on 6 pairs of black trousers - they were rubbish fabric and lousy cut/fit. I still have one of the old pairs but it is beginning to look a bit worn. Maybe they aren't doing them anymore because they were so good and didn't need replacing very often!
Other big whinge is swimmies. Again about 12 years ago I had M&S swimmies. one layer of fabric, underwired, DD cup, no padding or tummy control. They were so comfortable, looked as good as a swimmy will on me and lasted! When the time came to replace them I ordered on line two of the new range. My daughter and I fell about laughing when we unpacked them. they were garish in colour and the preformed DD cups looked like those silver cloches that cover up roast turkey. Needless to say they went back. I am for the most part in a swimmy during the summer, I don't want padded cups or tummy control (even in the sun the under layer gets uncomfortably cold as it doesn't dry quickly). My swimmies don't last because of being in a lightly chlorinated pool several times a day so I am always on the search. At the moment BHS bagain swimmies fit the bill and are really cheap, so must stock up in case they change.
I like their knickers, but the bra fit seems to change. 10 years ago it was fine, but now they are no good.
Longer T shirt length. and skirts that are panelled, calf length or longer for summer and winter. These are so much more elegant on older ladies.