Unless you grew up listening to early brit prog rock such as procol, genesis, etc... I'd suggest skipping the studio stuff and go for the better live efforts as the studio stuff can be an aquired taste.
The Great Deciever, Absent Lovers, and Vroom Vroom are essential imo
The Great Deciever has the killer early 70's Whetton/ Cross line up and while it doesnt have a huge variety it contains some awesome improvs! Whettons vocals are great as well
Fripp is one eccentric dude and what I like about The Great Deciever is how he was always complaining how it was hard for him to play over Whetton and Bruford!
He reminds me alot of Frank Zappa in his approach to composition and CONTROL haha
Absent Lovers is the excellent Belew/Levin line up, has good variety of songs and Belew's singing is in top form. Brufords electric percussion kit from that era still makes me cringe! What the hell was he thinking? Larks Tongues In Aspic pt 2 is always insane but this version is probably my favorite
Vroom Vroom is a more modern Double Duo Belew/Levin/Gunn/Mastelotto incarnation and contains much newer material and highlights many of the favs from the entire library
LIVE is where Crimson can really blow your hair back. I find most of their studio efforts to be rather plodding and dull in comparison
If you're not familiar with Zappa's live 70's library then you might want to spend some time there as well....AWESOME
Start with "Roxy & Elsewhere"