I've been riding there many, many times. I love its diversity: decent-sized sandy dunes separated by whooped out trails and areas dotted with volcanic ash, gravel and pumice stones (leftovers from Mount Saint Helens blowing its top in 1981). If you want mud you can find it there too - even in the summer.
Perhaps the best part though is the lake itself; it's huge and perfect for fishing, boating, cooling off in, or just going to, to stare at wet, bikini-clad titties.
I've yet to find a place anywhere else that offers all the Moses Lake dunes does. That typed, the place starts to feel small after you've discovered all there is worth finding. As long as you keep in mind how rare places like that are - especially in Washington state - and understand they are not at all 'sand dunes' (if you define a dune as being what is in Oregon) you'll have a blast.
