Couple of differences - Walther got rid of the slide's top cover (huge improvement!), new style frame mounted decocking lever that doubles as a slide stop release, neat firing pin safety - the firing pin's back moves up and down, resting on slot cut in the hammer when in "safe" position. It still uses the P38 locking system and the back mounted twin recoil springs. Some of those upgrades were incorporated already in the P4 model, but the P5 was a more refined, modern style compact pistol. The P5 still uses the heel magazine release, while the P5 Compact has a side mounted button one, but I personally have no problem with the first. It's a neat gun, but the fact that it's out of production, it was not widespread and the high build quality that was typical for Walther at that time command the high prices we see today.