The nature of the weapon is defined by the engine you use. Engines on offer include things like military, plasma, tesla and incendiary. Use a military engine and the weapon will fire traditional bullets, use incendiary and it'll become a full-fledged flame thrower.
You can then further tweak your weapon by picking what tip and upgrade to use with the engine. Tips alter the nature of the weapon, deciding whether it will be long, mid or close ranged in focus, while upgrades serve to improve things like its reload speed or firepower.
Most frames can take two engines, a higher and a lower, thus offering you two fire modes on any gun you create. This means that you can create a mixed weapon bespoke designed for any situation.
For example, in one section of the game we found ourselves in a dark spaceship corridor where Necromorphs would regularly try to get the jump on us by lunging out of dark corners in close proximity.
When our first try at going through with a regular assault rifle proved nearly impossible, we simply went back to a workbench and tweaked our weapon to include a shotgun fire mode, thus making the close quarters combat section a breeze.
Isaac's improved combat prowess is further demonstrated in the increased movement and cover options Dead Space 3 offers. Where the original Dead Space games made you feel very slow, with Isaac's armour giving the impression you were permanently weighed down, Dead Space 3 makes you feel fairly spry adding roll, duck and even full on, Gears of War-like cover mechanics.
This all adds up to make you feel far better equipped for dealing with Necromorphs and hostile cult members than you did in the initial games. While some will lament incurring the loss of tension Isaac's increased prowess results in, we still found Dead Space 3's combat a blast.