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In the final comic of the web series 百日後に死ぬワニ ("The Crocodile Who Dies After 100 Days"), which you can access here if you don't mind the spoiler, the crocodile receives this final message:
How should I understand「よくね」? How would the meaning differ if it was 「いいね」 instead (the translation I would expect)?
よくね？ = よくない？ = "Isn't it nice?"
As for this particular word form, it is a relatively recent slang in casual speech. This ね was developed from ～ない？ which functions as tag question "isn't it?", thus always carries a mild to acute uptalk intonation, whether or not written with a question mark.
Its grammatical construction follows the etymology. That is, [noun/na-adj] + じゃね？, [i-adj] + くね？, and [verb]-未然(nai-stem) + ね？ (in which case means "why don't —?").
The most remarkable feature of this expression which is not predictable from its origin is the completely flattened phrasal accent.
いいんじゃね{LHHHHH}？ vs いいんじゃない{HLLLLLL}？
やばくね{LHHH}？ vs やばくない{LHLLL}？
かえらね{LHHH}？ vs かえらない{LHHLL}？
(the effect of question intonation is excluded; all examples have a rise in the last syllable)
This effectively yields a straightly upward phonetic realization, very much close to that of an English yes-no question sentence.
This よくね is not よく + sentence ending particle ね, but よく + ない, with the dialectal pronunciation ねえ shortened to ね.
