I do really high mileage (95-110 per week) only for about 4 months out of every 18 months when I'm either training for a marathon or just trying to increase fitness. During this time I usually hate the long runs. I would say that probably 1 out of three runs over 15 miles for me are enjoyable the whole time. Once in a great while (1 out of 10 long runs maybe?) a long run is great and I run it while thinking the whole time that I can't imagine wanting to do anything else.
The only people I know who love to run and look forward to every single one of their runs are people who run about 3 miles a day. Proper training for a 10K even and on up requires the daily grind including the long run, and it is a pain in the ass sometimes. No one said running had to be fun all the time. It is hard work. If it weren't, everyone would be doing it.