Bittermens liqueurs (and bitters) are all amazing! They are all very different than most products out there. Most are recreations of products not available in the US, or ones that haven't been made for more than a century.
I have used all of them in creating various cocktail recipes and try to place most of their line in all bars I consult to.
All are really bitters based. Everything they do is. That's one of the things the Bittermens team (Avery & Janet Glasser, and Mayur Subarao) are known for.
The Citron Sauvage is a bitter grapefruit liqueur. It works well in any cocktail that has grapefruit as an ingredient, and substituted for citrus liqueurs in cocktails and brings a new twist to them.
The Amer Nouvelle is a bitter orange and gentian liqueur, plus assorted spices. It works well as a substitute for Campari and Aperol, but goes in a different direction, maybe a bit more complex in some ways.
Amere Sauvage is a gentian based liqueur with floral notes from chamomile and citrus peel. Very bitter but very complex and well rounded.
Hiver Amer is a cinnamon liqueur with bitterness from gentian and bitter orange. It is pretty unique. It works very well in variations on tiki drinks that call for cinnamon syrup.
For the heck of it I played with all of them in Negroni-esque creations, replacing the Campari. I came up with some pretty great drinks, all on the complex bitter side, but really need to sit with them to play in more detail. I don't have any of them at home to work with, so it will have to wait until my next consulting gig.
If I was only to get one of their products it would probably be the Amer Sauvage, then Hiver Amer second.
They also have the New Orleans Coffee liqueur which is more bitter than other coffee liqueurs, and more intense, but balanced with chicory and just enough sweetness.
Their Baska Snaps is really good too. It's a aquavit liqueur made with caraway, licorice, citrus and herbs, and some wormwood spirit. Very complex and unusual. I haven't played with this at all in cocktails yet, but have had it on the rocks and liked it a lot.
I'll look for my detailed notes from my last consulting gig. It's just finding them... I recently moved all my old files and unused equipment to a larger, temperature controlled storage unit and quite a few boxes are buried behind the distillery.