Really. I've heard people say "Reaper Man", "Mort", "Small Gods", "Wyrd Sisters" and "Interesting Times" but never "Guards! Guards!".
Well, live and learn, eh? Just check out the forum link I put at the end for numerous examples.
I just wish that the writing felt as polished as later on and the jokes landed better.
I feel like the "polished" period kind of cuts both ways, myself, because whilst the actual prose improves, and the jokes do land more successfully, a lot of the characters become less convincing, and less satirical, with Pratchett really 150% unable to "kill his darlings" - and I'm not saying literally kill them, like, make them look like idiots/screw-ups/fallible, which weakens a lot of the satire and even makes some of the moralizing seem dodgy because they become increasingly superhuman/infallible. There's also the issue that people who are really horrible or spooky individuals start getting regarded with fondness rather than apprehension (like Vetinari). The moralizing is particularly an issue, because whilst it gets better-judged - i.e. less "Stop the book, time for a moral!" and more justified by the events of the book and less "Uncle Tezza is here to set you straight", which is good - the characters delivering the morals becoming increasingly infallible (and in a couple of cases, and yeah I'm looking at you, Weatherwax, even a little smug and superior, rather than "truth-telling"), which is bad and makes the morals seem much cheaper.
The formulaic-ness of the novels becomes more obvious, too, and he increasingly leans on "ripped from the pages of history/20th-century pop culture" rather than "inspired by fantasy" (I think some people actually strongly prefer that, but I don't - I admit it probably helped the books succeed though). Additionally, the twee-ness/saccharine-ness of some of the later Discworld stuff makes my teeth hurt (and the failure to "kill your darlings" exaggerates this).
Death becoming a central character is pretty much an example for literally everything except the "ripped from the pages of history/pop-culture", I note.
I'm always slightly torn on criticism of The Colour of Magic, because I feel like easily 90% of people who really don't like it do so because they just aren't familiar with what it's satirising, and they jokes don't land for them because they profoundly don't get it. That's also why I think a lot of the "ripped from the pages of history/20th century pop-culture" stuff is extremely popular, even though some of it is kind of weak/uninspired, because it's more accessible to a broad audience, one which is unfamiliar with fantasy. The City Watch stuff is the particularly well-regarded because it exists in the crossover zone where it's accessible enough that a general audience who doesn't know fantasy "basically gets it", and it also works well for the more fantasy-oriented audience which was the original Discworld audience (and is still a decent-sized chunk).