A lot of box stores are starting to offer decent entry level bikes. The only problem with the box stores are lack of knowledge which leads to bicycles that aren't properly built and tuned. Not to mention lack of real customer support, fitting services, different size bicycles, and other support. Don't expect a wal-mart employee to true that wheel or replace broken spokes, adjust the brakes, or even apply quality bicycle chain lubricant.

If you can forgo the above and assemble and tune it yourself then go ahead. Also, grip shifters tend to break quite easily or they don't offer smooth shifting compared to rapid fire/brifters etc. Big box store bikes usually skimp on simple things like nuts and bolts which tend to rust.