I'm going to chime in as someone who loves the game and spent a long time playtesting GURPS stuff. First, it feels like it's been played a lot. But it doesn't feel like it's been widely played.
Just tinkering with the rules as a reader and would be player, they work. But they require some thought and interpretation. As well as some familiarity to know where things are in the file.
It could really use a quick and dirty summary set of pages, a table of contents and an index.