You know, I saw this bike at Wal-Mart a few weeks back. I pulled it down off the shelf and gave it a good once-over and I do remember thinking a few things to myself that would probably be of use to you, but I can't for the life of me remember what those things were. I do remember that it's a nice step up from the $150-ish "GMC Denali" model.

I may be wrong but if memory serves me correctly, your bike may have a cheap freewheel rear hub, which means you could break or bend the rear axle (wheel) if you're heavy and/or ride it a lot. Fixing that is as simple as buying a cassette (the gears on the back) and a rear wheel designed for the cassette if the original rear wheel starts having problems.

Best of luck, and keep on riding!