I try not to think too hard about ratings because I think they're generally more useful as a conversation-starter than a hard set point, but on a five star scale it's vaguely...

1 or less - Incoherent. Either no effort went into the project, or those working on it just lacked the technical knowledge to make anything work

2 or less - Clear artistic intent, but a still-obvious lack of competency. Conversely, technically competent but soulless or ill-considered

3 or less - Average overall. Worth watching, but lacks characteristics to really distinguish itself from others, or has strong/interesting ideas, but ultimately fails to deliver

4 or less - All the marks of a well-made film, and interesting enough to really remember. Anything 4 or above I'd be happy to rewatch or recommend practically anywhere, anytime.

5 or less - Outstanding in all or most aspects, always worth watching. I generally think that the difference between a 4 and a 5 is really just personal resonance, as anything above a 4 should be overall already be technically and artistically sound.