I'm sure 1.5 will have at least two or maybe even three new features in it. But if it was only going to have one, and you got to decide, what would you add to the game?
Shotgun explosive ammoWeapon Mechanic overhaul in conjunction to what Ian said. Daggers are useless because you have to get up close and personal with the monster, but you lack any sort of mechanism to Dodge/Block/Perry/Save yourself. Hammers are lack luster in terms of choice, but they do have a nice mechanism. Slingshots are way too difficult to control.
Personally, Slingshots would be nice if there was no "pull back" mechanic. Maybe a simple click-hold charge to determine how far the projectile travels, or a simple fire-and-forget with no charge, and the projectile will have a consistent amount of travel time. Could also make ammo that results in the projectile having a bounce, or arc.
Right click could be an inefficient shatter shot, firing multiple projectiles in many directions in front of the player, and where they go is determined by RNG. This could give the option for a range-like player to get up point blank to a monster in attempt to do heavy amount of damage real quick. This may seem like "Dagger weapons but ranged", but the big difference is that this is a choice for the player, if they wanna use the weapon in this particular fashion. They can still be ranged when using it. Up close and personal is a requirement with the dagger. This type of mechanic could also be an "Oh crap" button when a fair amount of monsters are coming at them, all at once. Like those damn Serpents.