Giant is definitely a respected brand, I don't know about that particular model. It looks nice in the picture. Plan on $35-50 dollars for new tires and tubes. If you are not "bike handy" you should also factor in the cost of a tune up which could range from 50-150+ dollars depending on level of service and parts needed.
As for hybrid vs mountain bike, the geometry and stock tires are the giveaways. A more upright geometry with smooth tires would make me think hybrid. If it's got knobbies, it's probably a moutain bike. These are generalizations.
What are you planning on using the bike for?