na-adjective
Used to describe harsh criticism or treatment, often with verbs like 言う, けなす, こき下ろす. Conveys a strong, negative evaluation.
See also: くそみそ
彼は私の提案をみそくそにけなした。
He harshly criticized my proposal.
ネットでみそくそに言われて落ち込んだ。
I got depressed after being scathingly talked about online.
na-adjective
unable to tell good from bad; treating everything the same
Describes a situation where valuable and worthless things are mixed or treated without distinction. Often used in the phrase みそくそ一緒 (lumping together the good and the bad).
See also: くそみそ
あの批評はみそくそ一緒で、良い作品まで悪く言われている。
That review lumps everything together, even criticizing good works.
If you're treated without distinction (between good and bad efforts), you lose motivation.
くそみそ is a synonym with the same two core meanings (harsh criticism and mixing good/bad). The order of elements is reversed, but usage is nearly identical. みそくそ is slightly more common in modern casual speech.
Compound of 味噌 (miso, soybean paste) and 糞 (kuso, feces), literally 'miso and shit'. The juxtaposition of something valuable (miso) and something worthless (feces) gives rise to the meanings of harsh disparagement and inability to distinguish good from bad.