Im getting to be a bit of a regular over the chase. I have only ever done follow the dog (easier trail), as Im not a great climber and they climbes on the monkey trail (harder) are, erm... much harder.
Its difficult to say how difficult they are as it really depends on your skill level. To start with I found it tough, now I still finds it a challenge but not scary as I know it so well now. Although I haven't MTB anywhere else I have seen lots of videos and I would say if you are happy doing Sherwood there wont be anything on the dog to upset you, but some of the black sections on the monkey may be worth a reccie before attacking them.
This page tells of any sections that are closed...
http://www.forestry.gov.uk/forestry/INFD-9FJCXA
And you can see videos of most sections here...
https://www.youtube.com/user/ChaseTrailsUK/videos
Also worthy of note, "Son of chainslapper" is now open, a loverly bermy rollercoster that's over far too quickly!
Does it get busy? Oh yeah! A dry weekend will be busy, on a dry bank holiday Monday it will be heaving! A mix of people from XC racers to people with there
Halfords £99 bikes.