What is the most interesting grammar in Lojban?

The harder bits. ๐Ÿ™‚ In particular:

* The fine differentiations in aspect and tense, including Lexical aspect (achievement, event, accomplishment, state). Hard to speak, not sure how successfully they’ve been taken up, but fascinating.
* The abstraction particles: Events, Qualities, Quantities, And Other Vague Words: On Lojban Abstraction. Even more fascinating, even harder to speak.
* Raising (linguistics) constructions, and the eye opener of how prevalent they are in natural languages: Events, Qualities, Quantities, And Other Vague Words: On Lojban Abstraction [tu’a, jai]
* The genuinely eccentric ๐Ÿ™‚ approach to anaphora
* Like James Wood said, the open-ended case roles/prepositions, and their kaleidoscopic version of case grammar
* The argument structures of compounds (lujvo), which was more case grammar, and which I may have had a role in advocating: seljvajvo – La Lojban
* The text structure markers, which I found neat, at least in writing ๐Ÿ™‚ Putting It All Together: Notes on the Structure of Lojban Texts

The attitudinals and tenses, actually, not so much: they were quite attention grabbing, so I didn’t find them as appealing. ๐Ÿ™‚

The logical connectives were most useful to me in demonstrating how littleย  natural language connectives have to do with truth-conditional logic. ๐Ÿ™‚ If is seldom translated successfully as ganai.

How did your life change after learning Lojban?

Gave me a podium to be a language pioneer for a little while. I gather I am still revered in some circles as the first fluent speaker. ๐Ÿ™‚

Gave me a severe sequence of intellectual challenges at a time when I needed it; helped me sharpen several of my skills, including writing in English. ๐Ÿ™‚

Made me a linguist and not just a linguaphile. The emphasis of Lojban on formal semantics (not just formal logic) made me more acutely aware of language structure, and drove me to study it formallyโ€”even if what I ended up studying was rather fluffier (a common outcome for those who come to Linguistics from Computer Science).