I have run the Philadelphia Half Marathon twice and really enjoyed it both times. The expo is nice; lots of vendors and branded race gear, and bib pickup is a breeze. The start line can be crowded, and lines for porta-potties can be long, but there has been a heated tent in the past for keeping warm and waiting for the race to start.
The race loops through the city, showing runners the best parts of Philadelphia, before heading out to West Fairmount Park. Crowds can be thin outside the city, but local running clubs have big cheer zones and there's never a stretch without support. Aid stations are frequent and well stocked with water and electrolyte drinks, and some with gels.
The race ends by running past Boathouse Row on Kelly Drive and up past the Art Museum. The finish line is a party! Lots of spectators cheering and an enthusiastic announcer.