ExploderWizard said:
I totally agree. That was the first GURPS campaign that I played in and the first real taste of D&D to GURPS culture shock

Once I (not my character) broke out of mental stun caused by these differences the game was fantastic as were the many that followed.
There are a bunch of important differences to the general
feel of GURPS and D&D games (I'm assuming "medieval fantasy" as the genre here - that GURPS space opera games will feel different from D&D should be obvious). Here are a few I can think of at the top of my head:
- Faster rounds, slower movement: The characters won't be zipping around the battlefield unless the map is small. Especially if they are wearing heavy armor. So it's important that the PCs are already in tactically advantageous positions before the fight starts.
- Getting surrounded is a bad idea: In D&D, getting surrounded by mooks is just an invitation to use Cleave or even Whirlwind Attack (or their 4E equivalents). In GURPS, that means that some of your enemies will hit you, and you won't be able to defend yourself against this.
- Don't bring leather to a swordfight: Armor is much more important in GURPS than it is in D&D, since it directly substracts from damage. After two or three hits with a sword, pretty much anyone without armor will go down, but someone in plate armor will have suffered only minor injuries at best. So if you go into melee combat with weak armor, you should better make very sure that your defenses are very good.
- Easy to fall down, harder to kill: It's fairly easy to injure someone to the point where he will fall unconscious, but it is significantly harder to kill someone outright, especially if he has decent HT. This means that even if PCs go down, their odds of survival are actually pretty decent. Still, the
risk of death is never entirely absent, so PCs should still be careful.
- Greater Character Customization: That's the biggest difference. Not only does GURPS allow a wider range of possible character archetypes to coexist within a single party (for example, you could easily have both a youngster with lots of raw potential = high attributes and lots of advantages - and an old veteran, who has put most of his points of skills, in the same party without unbalancing things), but you could have some really strange races and other characters which would be considered "unbalancing" in D&D. For example, many settings have elves which are generally just plain superior to humans. This would be problematic with the D&D game mechanics, but not in GURPS - all it means that their racial template costs more, resulting in elves with lots of innate advantages, and humans with more skills and training easily coexisting in the same party. And then there are plenty of rules and advantages for social interaction which D&D hardly even touches - if you want to play a noble with his entourage, you easily can, and the rule system easily lets you nail down just what kind of privileges the noble enjoys thanks to his social status.