I can only speak as someone who has read the 'mainline' trilogy and did not realise that Galactic North was required (and I've still not read that). So I'd have to disagree with you about the 'closure' at the the end of AG - I found it pretty poor in a major sense and almost a cheat - thus GN had better supply something better! For such an excellent universe it came across to me as a pretty wimpy deus ex machina, just to make a tidy ending.
Don't get me wrong I loved the books and his imagination, (ok, there were some flaws - I might make a new thread to discuss those, as I'd have to litter my thoughts with spoilers), just that AG seems to get lost and sidetracked from the issue that he builds up excellently in RS and RA, the threat of the inhibitors. Either he just doesn't have the big novel story that took in what happened to the inhibitors, or he does and we should expect a fourth book at some point that dives in and gives a proper ending. If it is the latter, my view of the Revelation Space works might go from 'Excellent with some flaws' to 'Excellent'
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