I just got back last weekend from doing the Snowdonia Way. There is a choice of high or low routes, and I stuck to the high route throughout. It is not waymarked, and the instructions in the book were *mostly* enough to get me round on clear days, but I did need some map and compass navigation on days with poorer visibility. In addition to the book maps I also took the three OS Explorer (1:25k) maps, because I find them easier to navigate from, and I marked the route out with highlighter in advance.
I really enjoyed the high route. It takes in some superb summits - Cadair Idris, Moelwyns, Snowdon (groan), Glyders, Carnedds , and lots of great scenery. Worth noting that the high route doesn't always follow well trodden paths, sometimes they are faint to non-existent, or in a couple of places just cross country with no path at all, and these bits can be hard work and slow you down quite a bit. Overall I would definitely recommend it though, it is fairly new but I think it will be quite popular once people get wind of it.
Just writing up a trip report, and I'll post some pics and a link once I'm done!