GURPS like any games does have its limitations and weak areas. Many other games share similar weak spots so please y'all don't take this as ragging on GURPS only as pointing out its weaknesses.
#1 Bestiary/Book of Adversaries
GURPS really needs a book of adversaries . Not just D&D monsters but everyday foes in a plethora of settings ranging from Tl1 infantry to Tl12 police and with common critters as well.
GURPS is not very good for vehicle combat. Its great for infantry fights even futuristic and modern , tolerable for horse mounted battles but not great for any kind of vehicle combat whether it be modern war, chariot battles or spacecraft. It works and its abstract systems can be fun but its not something the game is meant to do or as yet does well.
GURPS does have a rudimentary "your stats mean X" system but its sucks for determining things like "how do I compare to a typical man at arms or soldier or cop or professor or whatever." This is kind of a product of a lack of a books of adversaries as much as anything.
#4 Supers Design
GURPS has come a very long way since 3rd edition and its current rules (GURPS Powers, GURPS Supers) make Supers viable mechanically but its not easy to build powers or to use things like the Handbook of the Marvel Universe to benchmark ones own characters. If I wanted to play say a knock off of a certain web spinning guy who can lift 10 tons or a certain metal dude who can manage around 75 and bounce artillery shells or just a guy with an eyebeam whose power can punch through one inch of armor at 2 feet its surprisingly hard to do . Its also hard to make a good super quickly though templates do help here.
GURPS even with the 4e upgrades and the awesome T-Bones Gulliver doesn't handle scale well either very fast characters like speedsters or heck a mundane cheetah big ones, GURPS attack on Titan or Shadow of the Colossus would not be optimum nor would GURPS the Littles or Bunny And Burrows 4e be especially mechanically sound . really small ones. It does though children and young PC's surprisingly well , it doesn't benchmark skills but its otherwise not bad and GURPS Lashings of Ginger Beer or Rugrats could work
The Return of Planescape? - Curious. There is a brief note on this 'countdown' at Enworld.
15 hours ago