What do you REALLY think of the Kirby vacuum cleaner?

I have known about Kirby vacuums forever...My grandmother had a Heritage 84, which was ped down to my aunt and is still running smooth. But here's my question...are they all they are cracked up to be? I don't mind the changing attachments or buying a more expensive bag, but do they honestly clean better than an average Hoover upright from Wal-Mart?