i think m & s are great. i've always found their packs of knickers to be good value, a good fit, and good quality, same with their bras. their basic t-shirts are good value too, i've some which are maybe 8 years old and worn regularly. they're only a few £££s each.
i also like their linen tops which are a good fit for me. linen is what it is, creasy fabric, but personally i don't think it detracts from the garment and rather like the crumpled linen look.
doesn't mean to say i don't buy stuff from other places too though. i buy what i like and what suits and fits me, doesn't matter where it's from. i've some really nice linen things from matalan, and cotton pedal pushers from there too, and BHS.
personally i think m & s are still very good quality.