The medium (new model) tablet is the first wacom accessory used, and is very accurate and easy to use. Sensitivity is good and the driver/utility software is robust.
Two things in use do niggle though.
The first and most annoying is the supplied USB cable is really short and it is also recessed so you have to use it, because normal micro-USB cables will not fit.
The second niggle is there is no bundled software when compared to the previous model. These devices are not cheap, so a bit of user software would have been welcome.
Overall though, it is a quality peripheral and is easy to use.
If you need to know the actual size ... there is an inner and outer area, but how these work on your desktop can be configured depending on your desktop size and if dual monitors (i.e. you can set the tablet to fit your desktop or just part of it).
Physically, the inner area is 215mm wide and 135mm in height (landscape). The outer area is 270mm by 165mm. This inner area is marked on the tablet by four small "dents", one in each corner (a bit like you get from a centre punch) to signfy the inner area.
Having now used this for about a month (mainly with GIMP), it has been more a joy to use with time. The key point is that you need to spend time with the device and set up your image edting tools to suit. I've also become used to the ability to use as a large touch-pad as well.