First, is it too late to return the bike? Or maybe trade it in on something else? If you really don't like the bike itself, that might be worth looking in to.

If you like the bike in general, and it's just the shifter that's throwing you off, that's a fairly easy fix. Shimano makes some nice trigger shifters that your LBS could switch for you. (try a bike with trigger shifters before you change, though!)

I like grip shifts for commuter bikes. They are simple and elegant and you can run thru multiple gears at once. You can also try to retrain yourself not to pull so hard on the bars when you pedal, and to down shift sooner on hills so you can use your legs rather pulling with your arms.

I get the feeling from your post, though, that it's the whole bike that is bugging you.

Maybe it's time for a faster lighter bike?