As you can probably guess, weapons are important in "Dead Space 2." You're likely to find that some weapons are more useful for battling undead flesh than others, however. Apart from basic descriptions of each of the games weapons, we'll be listing that weapon's overall usefulness.
If you're looking to collect all of the weapons in the game, be sure to open up any power node doors you come across, as they often contain schematics for new weapons, along with large caches of money and ammo.
NAME: Plasma Cutter
DESCRIPTION: Returning from the original "Dead Space," the plasma cutter acts as a pistol which can cut the limbs off your enemies with ease. Secondary fire rotates the aiming mechanism, allowing you to fire horizontal or vertical shots, depending on your target.
USEFULNESS: Very, very useful. Arguably the most versatile weapon in the game, the plasma pistol can handle many different situations and becomes devastating once upgraded. Never leave home without it.
NAME: Line Gun
DESCRIPTION: Like the plasma cutter, but with a much wider attack line. Secondary fire unleashes a powerful, timed explosive.
USEFULNESS: Rather useful for large, heavy enemies, as you can take out multiple limbs with one shot. Slow-moving enemies can also be devastated by the secondary fire. Limited, expensive ammo means you'll have to pick your shots, though.
NAME: Pulse Rifle
DESCRIPTION: Basically an assault rifle which can take out crowds of small enemies very quickly. The secondary fire has changed since "Dead Space 1," and now fires a grenade projectile, causing a large swath of splash damage.
USEFULNESS: My personal favorite for crowd-control, especially with small enemies. Upgrade the clip size and you'll be able to make it through large encounters without having to reload. Ammo is plentiful and cheap.
NAME: Javelin Gun
DESCRIPTION: A gun which fires highly-damaging spears. Secondary fire causes the last fired spear to electrocute nearby enemies.
USEFULNESS: Slow fire and reload times makes this good for large, predictable enemies. The secondary burst can take out smaller packs, but it can be risky as you can become surrounded very easily. Good for long range.