Episode 2 went a long way toward making the weapons a lot more "visceral" to use, I think (and I use that in the most literal sense possible, guts!). While the blood sprays and antlion gibbing look over the top to some, they leave no doubt in your mind that you're hitting your target and that you're doing significant damage. In those regards it's a much better feedback system than what was in HL2 and Episode One, which was often missed by the player altogether.
I wouldn't mind a retooled gore system a la Left 4 Dead 2 appearing in Half-Life 3, with some tweaks. Combine Soldiers and Synths wouldn't gib easily on account of their armor, whereas the lesser antlions and zombies would gib often. Oh, and you'd be able to finally crowbar headcrabs into goop again!
Oh, and I'm a total Crossbow fiend. Love the feel of the weapon, it's just satisfying to overcome gravity and nail a long distance shot, and to adhere your target to the surface behind them on top of that. KSHNK!
The Magnum, Shotgun, and Gravity Gun are in the tier below it for me. Learning to zoom-snipe with the Magnum turns it into a genuine sniper rifle, and this can even be done without a crosshair with practice. One of the more enjoyable weapon skills in the game for me. The Shotgun can be relied upon virtually anywhere so long as there's cover and middle-ground, and letting off both barrels and taking down an enemy in one salvo is most enjoyable. And of course there's the Zero Point Energy Field Manipulator, which is hands-down one of the favourite tools I've laid hands on in a game. Versatility is what it excels at, I can haul extra munitions or supplies, I can turn rubble into weaponry, or use such defensively to shield myself, I can impede enemy movement with it, and under certain conditions I can kill enemies with it directly and use their corpses as kinetic ammunition. Further, I have ample reason to love the sort of novel physics-intensive combat that it directly or indirectly inspired.
The AR2 more or less straddles between the good and unremarkable weapons for me. The accuracy is nice to have, but there's something missing from the operation of the weapon. I'm thinking a heat wave distortion effect in the air around the gun whilst firing would be a nice touch, and the alternate fire disintegration effect could use some love in HL3. Portal 2 retouched its own disintegration effects beautifully, incidentally.
The Pistol and SMG certainly could be a lot more engaging to use, but outside of redoing sounds it's a tricky question. One wouldn't want them to usurp another weapon's role in the "sandbox" needlessly. A twist to their alternate fire modes might do the trick.
The SMG's alternate fire mode is already fairly enjoyable, but I wonder what element could be added to increase its appeal. Perhaps holding down the trigger could enable a timed grenade mode, glowing red and expiring some sort of timer before exploding. Frag Grenades in turn could perhaps take on some sort of new anti-vehicle function in addition to their uses against ground troops (slowing down Synths could be a useful function).
The USP Match (pistol) doesn't have an alternate fire mode to begin with, but I'm immensely curious about what it'd be like to partially merge its function with that of a weapon cut from HL2's own development: the
Flare Gun. It'd be the sort of thing that players would love to have on hand with Zombies and Soldiers about, but it would be easily balanced too by the necessity of collecting flares from the environment. You could even work unique gameplay sections out of it, such as running around in a zombie hell level with scarce pistol ammo and timely flare caches.