There's nothing wrong with that bike for your stated primary purpose of commuting. A road bike is going to be lighter, probably geared differently, and more "efficient" to ride, but as has been stated already, for a reasonable commute, I wouldn't hesitate.

In fact, I commute 8.5 miles each way on a mountain bike with slicks. I like the upright position it affords, and it's actually more comfortable on the rougher sections of city streets than my road bike with high pressure skinny tires.

If you've got it, ride it and don't worry about what somebody tries to tell you.