Never cared much for Lucifer's Hammer last time I tried to read it. Maybe I'll try again.
The Mote in God's Eye, while a different genre, but by the same authors, is fantastic.
Yea, now *THERES* the ultimate SHTF scenario... moties get out of the mote and actually start spreading into human space.....
(The follow up to MIGE is The Gripping Hand by the same authors, another really good read. )