Full disclosure prior to opinion: I am a mechanic at a bike shop. So if you want you can take my advice with a grain of seasoning of your choice.
In my opinion bikes from wal-mart are ****. Being dangerous, poorly put together, cheap, heavy, no support from a professional service from the location you bought it (translation: wal-mart has no mechanics only sales-droids), no warrantee to speak of and they drive legitimate (and helpful) bike shops out of business (not to mention any other business). In fact, I would say that avoiding ALL department store bought bicycles should be the norm.