have done this one twice and it is a nice run, probably a bit more hilly than you think while running - if that makes sense but there is one large ish hill you go over a couple of times, but the drop on the other side is quite steep so you can rest/recover a bit on the way down.
The Greenway is the main talking point as usual, on the first lap it will seem quite pleasant, nice straight and flat run taking you close to the half way mark, there are also a lot more runners at this point who break off to the half marathon finish. The second lap can be a different story though, the Greenway section is much longer (around 5 miles from memory) and by that time in the day it is usually much warmer, there are less people out there and of course you are in miles 20-25 of a marathon so the going is much tougher.
Having said all that this is just my experience and some do like the fact that the Greenway is flat and straight and means you must be nearing the end! Just seemed a bit too long for me second time round. If I could choose I would reverse the course and get the Greenway sections out of the way earlier in each lap.
The organisation was good and Stratford is great, stayed at the holiday inn both times which is right on the start line and has a jacuzzi for after the run.
Seems to be two threads on this so will add this to both