Another one who 'broadly' followed the 18 week 55-70 mpw schedule. I say broadly followed, cos I always had Tuesday as a rest day (for family reasons) and P+D have a quality session in there. So I ended up jiggling it round a bit, but mostly did the sessions. It helped me to run a 15 minute PB - 3'12 to 2'57, so thumbs-up here too.
If I was doing it again I'd make sure I did all the Mara paced stuff they advocate. Too many of my Long Runs were time on feet jobs. Yes you need these to build an aerobic base, but I didn't step it up enough later in the programme where I should have. You need to get used to running at 7'20 pace (for 3'15 say), and to get into the 'hurt zone' a little bit on LSRs. Not EVERY LSR by any means, but certainly more frequently than I did. I also did a lot more 20 mile+ runs than they advocate - 10 were 20 miles or over actually. I personally think some of the LSRs are a bit light, so I did extra miles (but then I felt I had a weakness in my endurance, so I tried to address it).
That's why I say broadly followed - work out if you have any weaker areas and try and address those as part of a solid programme - but don't be afraid to tweak it a bit to suit you.
Good luck 