I first read Jhereg by Steven Brust when I was a kid and fell in love with the voice and style of the books. Yendi is the second book in that series, though chronologically takes place before Jhereg. For those obsessed with reading in chronological order, technically the first book of the series would be Taltos, which I think was published fourth. If it all sounds like Brust was basically just making stuff up as he went along, following whatever story interested him at the time with little regard for the kinds of regimented series design we tend to live with these days, I suspect you're right. Maybe that's why the books hold up so well today.
Vlad Taltos is an assassin, but not the cool, nothing-scares-me, awesomely enigmatic variety that graces the cover of so many modern fantasy novels. He's just a guy trying to survive in a world hostile to Easterners (a.k.a. humans – the dominant species in this world are basically a kind of tall, long-lived, psychic, pedantic elves called Dragaerans who are exactly as big arseholes as they sound.) Vlad's pretty clever, good with a rapier, and hates the world he lives in just enough to make him good at surviving in it. Oh, and he's got a cool mini-dragon sidekick who calls him "boss" all the time.
The Taltos books are at once whimsical (though not in a Terry Pratchett way) and emotional (though not in the melodramatic self-righteous way of modern fantasy). They're stories that never seem over-written or even over-thought-out, but simply the artistic output of an author following his instincts and never worrying whether he's put in the required elements or checked off all the ideological boxes of the times. They're stories in the purest sense, which doesn't make them trite or lacking in message, only that the message is whatever Brust wanted to impart, never hitting you over the head, never worrying about whether you'll agree.
Usually when I try to re-read books from decades ago I find they don't hold up all that well. Either the language feels archaic or the tropes feel out-of-date. I didn't find that with Yendi. It reads, well, pretty much as it did when I was a teenager. I liked Vlad, liked the twists and turns, and never felt all that concerned with whether every plot device was entirely logical or not. Vlad feels real, so everything around him feels real.
Your mileage may vary, of course. We all have different tastes, but for me – especially in today's fantasy landscape – a book that isn't trying to follow conventions is a welcome respite. Yendi made me want to go back to all the others in the series, and start picking up the ones I missed in more recent years.