Zapping Combine soldiers with the supercharged gravity gun was a right lark, a fine moment in Half-Life 2. Today I've been larking around with a different type of turbo gravity gun in a new mod, and I think I prefer it. See, it lets me 'rocketjump.'
HL2 mod Transmissions: Element 120 [official site] is a short singleplayer mod introducing a new zapgun. It blasts balls of concussive force that send enemies and physics objects flying (and its levels are heavy on blastable props) and, of course, you. Look down, jump then blast a ball, and go sailing through the air like a beautiful murderous butterfly.
Transmissions is a whole mini-campaign of its own. I almost stopped early on, not enjoying more dingy HL2 tunnels with turrets and traps and wheels to turn and horrible black headcrabs, though one puzzle about darkness was neat. Then I found the super zapgun, or Zero Point Energy Projector to use its proper name, and was delighted.
I hadn't realised quite how much I've missed rocketjumping. Flinging myself across levels was grand, bouncing up and bursting through windows. It's a nice bonus that you'll also leave a trail of destruction as conveniently-placed objects near you will bounce and roll around crushing enemies.
The campaign's short (less than an hour) but has two great large combat setpieces in large arenas full of places to gravjump around and plenty of physics props to blast at enemies. The second one, especially, has loads of destructible environment bits to trash. It's jolly exciting.