The Edinburgh marathon is billed as being a fast course because it is mildly downhill from Edinburgh town centre to the coast. This is true and there is the potential to run a good time, but it is a boring course without spectators for the majority of the route.
The weather in 2009 and 2010 was also very hot (high 20s) which also made the event a lot more challenging and the organisers could certainly do with a few more water stations along the way. Plus the logistics at the end to get back to the town centre were not great.
Edinburgh is a great city though and could be a great place for a weekend break with the potential for a PB on the downhill course. Just don't expect crowds like London.