On the down side, the system is let down by antiquated (i.e. non-existent) marketing and the company's stubborn refusal to do anything else but put out more and more autistic, hyper-focused mini supplements that can only ever interest a small niche of GURPS experts.
Visually, the presentation is also very dry and soulless for the latest edition (Fourth Edition) when compared to the previous one. The layout and the tone of the text sometimes makes reading the Basic Set an exercise in willpower – but once you've gotten through most of it, it becomes very easy to reference and the rules are mostly clear and sensible.
Ideally, GURPS would need a new Basic Set that has better presentation and includes some of the more lightweight/narrativist options presented in various supplements to make character creation and GMing easier – more cinematic and vaguely defined skills, on-the-fly NPC creation, simpler combat rules – while cutting down or amalgating many of the less critical content. The length and complexity of character creation is systematically the biggest obstacle to getting new players to try out GURPS (unless the GM prepares pregenerated characters for everyone, but as a player I wouldn't even be interested in trying out an RPG where I can't create my own character). People also talk about the system being too crunchy, but that's really only because of the bad presentation. The core rules are very simple and you're not supposed to use every optional rule in the book – but you have to read all of the book to grok that, which is bad design.