The Chevron Houston Marathon is always a great race! It's the 12th largest race in the country so even late in the race, there are always a good amount of people around you. Despite the size, the race is very well organized with plenty of aid stations and course support. The sheer number of volunteers is staggering and they are all great. Lots of spectators come out to cheer the city on. And the pre-race expo and post-race festivities are great. As long as I'm in Houston, this will be an annual race for me!
Here's my 2015 race report: http://www.pathtotri.com/2015-houston-marathon-race-report/