This what I call a 'word scale' - a list of words that represent a kind of vocabulary spectrum, if you like. It's not easy trying to place Irish words in it, as according to the dictionary quite often some the words are more or less interchangeable as far as their meaning or 'intensity' is concerned, so I'd be grateful to have your suggestions about it. La voici -

brilliant - trop bien - ar dóigh ar fad

amazing - fabuleux - ar fheabhas

incredible - incroyable - thar cionn

fantastic - fantastique - iontach

really really good - super bien - ana-mhaith ar fad ar fad

really good - vraiment - ana-mhaith ar fad

quite good - plutôt bien - sách maith

not at all bad - pas mal du tout - níl sé ró-olc

fairly good - assez bien - réasúnta maith

not bad - pas mal - níl sé dona

good - bon - maith

OK - ça peut aller - cuíosach gan a bheith maíteach

not good - pas bon - níl sé maith

not very good - pas terrible - níl sé ana-mhaith

bad - mauvais - olc

pretty bad - plutôt mauvais - measartha olc

very bad - franchement mauvais - an-olc

really bad - lamentable - fíordhona

incredibly bad - affreux affreux affreux - millteanach olc

terrible - abominable - gránna

horrible - nul de chez nul - uafásach

absolutely awful - un désastre total - uafásach amach is amach

atrocious - atroce - ní fiú uisce na bprátaí é sin

a load of rubbish - n'importe quoi - truflais cheart chríochnaithe

I am afraid I am a bit rushed so I didn't actually look closely at anything
But I did not that you have forgotten that dona and maith require the go even when used as adjectives (aka: Níl sé go maith. Tá sé go dona)
sorry not to have anything more helpful to say

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Sometimes you don't need go: "Tá sé maith ag insint scéalta" (He's good in telling stories)

Go raibh maith agat, a Labhráis.
Ní raibh sé sin ar eolas agam go dtí anois

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ЯГОН ТОҶИК НЕСТ ИНҶО???