I visited London a few weeks ago and spent a good hour or so here and had a good time.
Our first stop was Wilde Maus XXL and I can honestly say this is one of those coasters that's just oodles of fun to be on. The queue is a really great distraction that got us all excited to ride, and the coaster was unforgiving with all the sudden drops and turns. 
Next was Olympia Looping which was another really great ride. The sheer intensity of it is great, and the whole ride is crazy for something that travels around a lot. The queue was virtually non-existant, so if it wasn't for the steep price, it would be hard to refuse spending an evening on it. 
Our final ride was Dr Archibald, and if I'm completely honest, I just didn't "get" it. Yes the theming is good and the facade is impressive and somewhat intimidating, but VR just doesn't do anything for me. I want to see the physical sets and scenes rather than staring at a screen- something I could easily do at home.
If you're in the area this Christmas it's worth a detour- it's hard not to enjoy yourself here.