SAMSUNG GALAXY I9003 - WHAT A SMART PHONE

I had purchased my I9003 phone 5 months back, which facing quite a many problems since day one, however these problems have now become intolerable, please help

Phone hangs all of a sudden
Have to remove battery every time it hangs
At times the phone takes more than 2 mins to restart
Phone heats up
The back button, nor the centre button works at times


I have been at the service centre at Nerul, Navi Mumbai, who knows nothing i guess, when i asked him on day one of my purchase why the phone is behaving so sluggish, he said I will reinstall the software.. . I this a solution...??

Is is worth buying a smart phone which isn't smart at all. . ?