A Cog in the Wheel is fun, odd, and quite memorable. The descriptions of Mechanus are wonderful, and the addition of the moignos is superb. This is really a flavor piece, like CORE 1-1, rather than a combat adventure. It continues the story nicely and is conceived as a means of introducing D&D characters to the variety and creativity of the multiverse. In that it is a tremendous success.
However, the adventure is a bit flat in terms of the actual plot, and it is too bad that we are not given a statblock for the Decaton, even just for the sake of amusement and curiosity. The lack of variety and depth in the explorable portion of Mechanus is also too bad. However, these are small criticisms. From a players' perspective and a practical play perspective, this is a nice, solid adventure that leaves a strong sense of lore and flavor and is quite of fun.
[4 of 5 Stars!]