I have to agree, interaction with other students is invaluable. I went straight from undergrad to MPH and the discussions with older students about their practical experience was enlightening. I had one online course - a terrible sample size - that met in person twice during the semester. It was my least favorite course. We had homework, online group discussions, and a group project, very similar to my land based courses, but something was missing. If you have to work full-time and moving is not really an option, then I guess it is a good substitute, but I'd much prefer land based to online learning.
That's my 2 pennies worth.