UFO - Tell me what I need to know

You must get:

Force It
No Heavy Petting
Lights Out
Strangers In The Night (which I don't have)
 
Here's what you should get:

1974 - Phenomenon [first album with Schenker it has the original version of "Rock Bottom and the album is great!]
1975 - Force it [The sleeve was banned in the US. Great album!]
1975 - No Heavy Petting [Even better highlights include: "Can You Roll Her", "Martian Landscape" and "On with the Action". An underrated album in UFO's history]
1976 - On With the Action [Live album without the title track!]
1977 - Lights Out [Seen by many as their best studio album. I bought it when it was released. Very good album]
1978 - Obsession [Good but not great. Still a must have Schenker shines on this one but the songs are not as good as on the previous albums]
1978 - Strangers In The Night [Their legendary live album. However don't start with this one. you'll appreciate this album much better if you already know the studio verions.]
1999 - BBC Sessions [Fairly recent release of several "Live in the Studio" recordings. Great sound quality!]

UFO was an amazing band in the 70s. Each and every one of these reconds is essential. Look for the releases that feature 2 albums on one cd. Very much worth having.

Let me know how you like the albums.