The San Diego Rock N Roll Marathon (hereafter called RnR---website http://www.rnrmarathon.com/) was my second marathon (Los Angeles 2001 was my first). It's a big marathon -- 20,000+ participants. A large number of those are
Team In Training participants (a group raising money for the Leukemia & Lymphoma Society) -- as such, it is a walker friendly marathon, with a time limit of 7 hours.
The course starts next to Balboa Park, goes through Hillcrest, around the park, to the Gas Lamp District, then goes on a freeway (that actually bisects Balboa Park), the 163, for several miles. You go around the bay that includes Sea World (though you can't really see the park). The last several miles are mostly alongside a freeway. (The course map is available on the RnR website.)
There is not as much crowd support as I experienced at the Los Angeles Marathon, in large part due to the fact that much of the course is on or next to freeways. There wasn't as much music as I expected, for the same reason -- stretches of miles where they couldn't set up. (The big gimmick for the RnR races are the bands playing every mile or so.)
Water/gatorade stations were about every mile or so. There was a power gel station at 17.6 but they'd run out by the time I got there (yep, I'm slow!). The volunteers were great -- gracious, friendly, encouraging. Porta potties were cleaner than could be expected and had TP even late in the race (always bring your own just in case!).
Overall pros: walker friendly for beginners, moderate crowd support, great city to visit anyway, relatively flat course, cool/overcast weather in the a.m.
Cons: course not as scenic as I thought it would be considering where it was. Parking at the finish was really far away without any shade for the walk (a mile or two, which seems really far, anyway, after doing the marathon!).
Although I'd recommend RnR once, I probably won't choose to do this marathon again -- too many other ones out there to try.