A group of us ride on Shotover regularly as part of our weekly night rides. For that it's pretty good–a lot of single track (more than some people on this thread seem to realize) crammed into a very small space which means that you're constantly going up and down. Apart from the three main bridleways and the old road across the top it's all completely cheeky and can be hard to find if you don't have local knowledge. There isn't anything that you might call DH though–one run with berms and drops, another with a couple of large log jumps but apart from that it's the kind of tight twisty singletrack that even I can deal with.
It might be worth a drive from Reading just for a change. To be honest, though, I don't tend to ride there during the day on a weekend because it gets too busy with walkers and dogs.