Actually UFO have one great album called Phenomenon. It would probably be put in my top 100 of all time! It was passed on to me by my older brother when I was like 9 so it's patially a setimental thing, but it's a really really solid album. I used to listen to it on my turntable and I wore the grooves off the thing. One of the standout tracks is Rock Bottom. I still love the record and have it on mp3. I'd describe it as hard bluesy rock. I've never heard any of the other albums except for a few cuts like Lights Out In London and Too Hot To Handle (both great songs). Michael Schenker, the guitarist, went on to fame in the Scorpions (who I do not like).
Edit: By the way Calcium, why do you ask about UFO?