I've done 15 units at GW and I'd avoid them if you have other options. They're one of the most expensive schools in the country, but that cost didn't translate into a better "product", at least for me.
One teacher I worked with was great, but the program I was in was disorganized and some of the teaching was pretty bad.
Hopkins is almost undisputed as the leader in International Health-emphasis MPH programs, and is right nearby GW. I'd highly recommend them based on numerous friends who have completed their IH program.
BTW - I left GW with great grades. I'm not some lazy slacker that didn't like the work. They just really aren't worth the money (especially considering the IM field - NOT a lucrative one).