User blog comment:Plexioth- xD/Monster Hunter 3 Ultimate/@comment-119.93.94.58-20121022090046/@comment-4976561-20121022232523

On the Greatsword: For level 3 charge you have to wait until an aura pulse to release otherwise will not deal full lvl3 charge. Element now charges up along with raw.

Lance: If you didn't play 3rd, they just removed the ability to counter after the 3rd hit.

Bowguns...

Light Bowgun: Rapid fires specific ammos like FU and P3rd. The new feature is the option to remove the Limiter, which, once removed will grant the ability reload all your loadable ammo in one action so you can switch between ammo types without having to reload them. It also gives a couple extra shots to specific ammo types depending on the BG. Note that doing so will remove the Rapid Fire ability from the gun.

Heavy Bowgun: Siege mode has been added, again, if you didn't play 3rd this is a new. The Limiter for the HBG does increase raw damage by a 10%, adds more ammo to specific BGs, removes the ability to Siege, and last but not least, adds the ability to load WyvernFire.

The Limiter can be removed and replaced at any time at the smithy for a cost.

Longswords: If you skipped 3rd, the only change is that the Spirit bar will deplete every time you do a Spirit combo even if you land the last hit.

And that's about it, and like Barrel Bomb said, Bow's arrow rain deals Impact damage which if used with a bow that has Focued Arrow Rain can be used to KO monsters along with Explosive Arrow.