ElliottB,
There is but one word to describe Lewisburg: quaint.
Do not expect much more. To say that Lewisburg's downtown is a joke compared to Chicago or New York City is to do a disservice to Lewisburg itself. You cannot even begin to compare cities like that. Lewisburg is not a city after all; it is a mountain town. It is situated at the intersection of Route 60 and Route 219 and is the wealthiest town in Greenbrier county. People come from the surrounding towns to do business in Lewisburg. You will notice tons of law offices, CPA offices, real estate agents and the like in the downtown area. You will also find specialty shops downtown, such as boutiques, outdoor shops and nice restaurants. You won't find many places at which to buy your day-to-day items. The downtown is really meant to attract tourists and to allow the folks from the more rural areas in the county to do their business in Lewisburg.
But honestly, I absolutely love it. I love to bike and my bicycle is my primary mode of transportation. If this is the case with you as well, then you will be just fine. It's quite a hilly, if not mountainous area, so you'll definitely be getting your workouts. But you really couldn't find a much better place if you like outdoor activities, especially cycling.
As Biology101 said, you will only be in Lewisburg for two years unless, of course, you choose to do your third year rotations right there in Lewisburg. It is important for you to feel like you live in a place that has things to offer you, like nightlife and social scene. It is important for us to get out and get away from the rigors of school. Having said this, as much as you will be studying, it will soon seem a little less important. As far as I'm concerned, I could stand on my head for two years if I had to. Two years is pretty darn short on the long run.
In my opinion, Lewisburg is great, and it worked out perfectly for my wife and I.