Alas, finals are eating up my time and I'm posting between writing essays. I'll give you a basic idea of how combat between two people would work.
In D&D, you roll your attack and compare to AC. If it meets or beats, that attack is good and you roll damage.
In GURPS, you roll your attack. If it succeeds, that means it's a good hit in danger of injuring your opponent if they don't successfully defend. They then roll their defense, and if they fail, you roll damage. However, unlike D&D, you have a huge number of options available to you just with attacking (there are more outside of it). For instance, you can aim for the face, trying to cause knockdown and stunning, or you can aim for an arm, trying to get them to drop their weapon, or aim for their leg, trying to make them unable to stand. You can try throwing out multiple attacks at once so they defend at a penalty if you hit multiple times. You can put all of your power behind an attack, sacrificing your defenses, for enough damage to get through armor.
Right, armor is DR, not a flat "can't hit me" number, so it reduces incoming damage.
You can throw away your defenses and make a more accurate attack, which makes you more likely to get a critical hit, or hit a specific hit location, or you can trade that bonus to hit in, penalizing your attack to penalize their defense. You can try to feint them, which lowers their defenses by your margin of victory in the quick contest. You can evaluate them for bonuses to hit and against being feinted. You can grapple them, and the grappling rules in GURPS are hands-down the best in existence. You can try to shove, either with a weapon or your hands or a shield, them to knock them over or make some distance between the two of you. You can use the dirty trick rules to gain the upper hand. You can focus on defense and give yourself a bonus to defend, or multiple defenses against an attack.
And none of the above require a feat to do, or even do well.