A bit rough around the edges, couple of things he (in my opinion, of course) missed, but not bad for a young ‘un (Mr Scalzi is two years younger’n me :-)
I can’t help but to compare OMW to Neal Stephenson‘s first book, The Big U. I really really like Stephenson, Diamond Age, Snow Crash and Cryptonomicon are highly recommended  — but The Big U, while having excellent ideas, is way shaky.
But let’s face it — I expect that from a first novel. And that’s why Scalzi rocks. If he improves like Stephenson improved, or for that matter like Pratchett improved , it’s going to be phenomenal. If he just maintains, it will still be good.
The other three books in the trilogy immediately found themselves on my Amazon wish list.
Now I’m into Parker’s Devices and Desires, the first of a trilogy. Someone recommended it, but I can’t remember who. Looks like it might be good.
 You have to be really into Stephenson to read the Baroque cycle :-)
 Go read The Colour of Magic again — it’s shakey :-)