As each episode ended it advertised the next and made them look so much better but never delivered and we were into a third before we couldn't watch anymore.
This is a bad sentence but is it technically wrong (stringing the phrases with the conjunctions). It feels like parts of it need structuring into separate sentences.
" It is still babbly and breathless, though, which is good if that's what you want, perhaps in rendering speech. The repeated conjunctions are a rhetorical device called polysyndeton (which works better here without the commas, actually). To make it more normal, I might chop it thus: "As each episode ended, it advertised the next and made them look so much better.
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Commas are needed in conventional writing:
"As each episode ended, it advertised the next and made them look so much better but never delivered, and we were into a third before we couldn't watch anymore."
It is still babbly and breathless, though, which is good if that's what you want, perhaps in rendering speech. The repeated conjunctions are a rhetorical device called polysyndeto