I thought it was a bit of a shambles. Not just minor improvements needed, but a major rethink.
The most serious issue for me was traffic management. I was nearly run over twice. The first time, at a mini roundabout, the marshall half heartedly put his hand up to stop the traffic and then put it back down again, letting traffic through despite the fact I (and others) were already on the roundabout. The second time I was waved to cross a road, despite the fact the traffic hadn't stopped (and didn't). I presume that if a marshall tells me that it's ok, then it is.
As others have said, getting to the stadium was a nightmare. A few people have said that we should've known that Oxford was bad for traffic. I live in Windsor. I rely entirely on the race organisers to give me advice, as I have no idea what traffic is like in Oxford on a given day/time. It should be reasonable to expect that arriving an hour before the event is plenty time, and it normally is for events I've attended up and down the country.
I appreciate it was the first year and there are always teething problems. I ran the Maidenhead Half Marathon three weeks ago with a similar amount of runners, which apart from the start, was really well organised, which proves that it can be done.