Liz - hope it went well. I just completed the marathon on Oct 16th and my comments would be:
General: Ignore comments about humidity etc - it was the coldest marathon I've ever done.
Plusses: cheap to enter (to be fair), interesting city to visit (although it had mushroomed in size since i was last there only 10 years ago), exhibition was good (if not easy to get to if you were based in the old city), great start location on the bridge (although if it been a nicer day...), good and frequent watering stops with some energy drinks on a few stands at the end and some fruit and excellent little sponges to cool off, nice goodie bag both at the exhibition and at the end, nice little certificate printed out at the end, good on-line data access, quite pretty first 10km and last 5km, rest of the time you could have been anywhere, very good tarmac thoughout with no cobblestones, atmospheric finish but why they ask you to climb a steep hill for the last 2km...., long boring (16k) section up and down the coast, and the bridge is a nice place to start (the raison d'etre of the race I guess) but the downer is that it is steep and then uphill after that and slows people down just when you want to speed up....etc,
Minuses: no place for a fast run - the uphill start, mid section and finish will stop that, very few km posts so hard to pace yourself and I am sure one or 2 were not in the right place, congestion at the start - after 33 attempts you'd have thought they could have ranked the start with anticipated finish times or maybe got some pace makers - but no - I spent the first 5km sidestepping slow runners and even walkers in the marathon race who had gone to the front, and then the slow 15k runners who were merged in - I had pretty much given up on a good time early on. Poor and inadequate toilet facilties (most portakaloos were closed bizarrely) at the start and non existent throughout the race, the bus pick ups were far too early for the start time so you hung about cold and wishing you had eaten more for breakfast, the buses were jammed and the 20 min ride not great if you were standing up, no atmosphere even at the end - partially due to the weather but apart from the last 100m at the square there were few spectators throughout - it was a quiet Sunday morning and you could have been out on a training run by yourself - especially as there were so relatively few runners... 2500?
Overall it was an experience - I would go back to Istanbul - and the organisers deserve a lot of praise but if you want a really well organised, fast, motivating and pretty marathon I don't think this is quite it.