Reamde is action-packed, intelligent, and full of scathing and hilarious observations on humanity in all its forms. It reads like a season of "24", but with more sophistication and character development. It may also be the first major work of fiction where a substantial portion of the action takes place in a World of Warcraft-style MMORPG.
That's my clean-room review. But since Neal Stephenson has been my favorite author for most of my adult life, I can't help compare this book to his other works.
Stephenson excels at fabricating fictional realities which have ties to, but are still alternate and alien to, our own reality. This may be in the near future (Diamond Age, Snow Crash), the past (Baroque cycle), or a world completely other from our own (Anathem)
I consider this approach the ideal form of speculative fiction. His unbounded imagination can step far outside the bounds set by our reality, and yet he keeps enough ties that it feels more real and has more relevance to the lives of his readers. This gives his work a level of sophistication above that found in most sci-fi, which favors far-future stories with minimally-explained aliens and technology which verges on magic.
Reamde is set entirely in the real, modern world, so I wouldn't even count it as speculative fiction. Instead of constructing an alternate universe, Stephenson uses the opportunity to explore the real world, including numerous cultures, from Chinese urban life, to American religious gun-nuts, to MMORPG gold farmers. Breaking from his usual approach certainly seems good for his growth as a writer, but I don't think the results are as good. (This probably makes Readme most like Cryptonomicon of all his books. I found that one fairly forgettable.)
Hence, Readme is probably the most accessible Stephenson book. There wasn't a single page I couldn't follow, unlike his sometimes nearly inscrutable masterwork, the Baroque Cycle. I found this both positive (it was easier and often more fun to read) and negative (less intellectual depth).
In summary: this is a fantastic book when judged on its own. But it's below average for Stephenson.