My completely subjective rating system:

91-100 – Whisky heaven, best stuff

86-90 – Wow, really good one, need a bottle

81-85 – Wow, really good one

71-80 – Fine, like to drink by time

61-70 – Okay, but not more than 1 Dram

51-60 – Drinkable, but really not mine

1-50 – Avoid it! Not acceptable