"I didn't read his entire post (it's very, very l-o-n-g), but from what I gather, he's a bright guy, as it was pretty well-written."
I disagree.
In the above sentence, 'well-written' is a compound adjective, yes, but it's a predicate adjective as well.
Am I not correct?
LOL. Where is William Safire when I need him. Given my druthers, I would have re-arranged the whole sentence, as your main 'subject' (post) is too far away and has another subject (bui) 'tween it, but as it stands I would simply have ended it with 'as it was well written' (and even that is rough). The conjunction tacitly needs a noun. The above reads a bit awkwardly, not unlike a dangling participle.
/ok. switching off grammar nazi switch.