I think it's rubbish because of :-
the lack of variety,
the abscence of technical difficulty,
the very low height,
the feeling of being cramped in,
knowing that every single trail has been noted and ridden,
not having anything there that scares the beejeesus out of you,
not having miles of sweet singletrack,
not having anything to test you physically,
being really ugly to look at,
not being able to ride somewhere in the park all year,
having huge crowds getting in each other's way and on each other's nerves,
there's no uplift,
it's nothing like a trail centre.
For all of these reasons and many more, Dartmoor is rubbish and as others have pointed out, nowhere near as awesome as it's near neighbours.