There are four types of Weapon Skills in System Shock 2: Standard, Energy, Heavy and Exotic, which correspond to the different categories of weaponry available in the game. The effects of Weapon Skills are twofold: they increase your damage output with a particular category of weapon by 15% per level, and they are required to pass the requirement check on many weapons in the game. Unless you plan to go melee-only, you'll want to put a good number of points into your Weapon Skills, eventually maxing out at least one of them.

Below, you'll find a more detailed list of the different Weapon Skills, including evaluations of each category.

Standard Weapons

Governs: Wrench, Pistol, Shotgun, Assault Rifle Maximum value: 6 Evaluation: Standard Weapons are your go-to for most of the game, with the Pistol and Shotgun being mainstays in the early game, and the Assault Rifle being powerful enough to take you to the very end, due to its versatility in ammo types and sheer damage output. Standard Weapons are reliable and effective in all situations, and while dependent on conventional ammunition, that ammunition is far more common than other types like Worm Clusters and Prisms. Unless you plan to specialise in one of the other Weapon Skills, boosting your Standard up to 6 by the middle of the game is recommended so that you can make full use of the Assault Rifle when it becomes available. Putting points into Standard is also useful if you plan on using the Wrench a lot, though you may want to avoid maxing the skill out if you want to switch to the Crystal Shard later on.

Energy Weapons

Governs: Laser Pistol, Laser Rapier, EMP Rifle Maximum value: 6 Evaluation: Energy Weapons are an interesting proposition - like the other Weapon Skills, it is a highly specialised category that makes a solid secondary focus for most characters, though due to the relative scarcity of mechanical enemies throughout the game, it pales in comparison next to Exotic in usefulness. Their main advantage is that they have absolutely no ammo requirements, but instead run off of a battery charge, so combined with Electron Cascade, they can be used without a lifeline to a Replicator, not to mention you stand to make a ton of Nanites by melting all that extra ammunition down with the Recycler. The major downside is that the ultimate Energy Weapon, the EMP Rifle, only affects mechanical enemies, meaning that you'll need to rely on alternative weapons for getting past the stronger enemies like Rumblers found late in the game.

Heavy Weapons

Governs: Grenade Launcher, Stasis Field Generator, Fusion Cannon Maximum value: 6 Evaluation: Heavy Weapons are a specialised branch, but the sheer excellence of the most basic of them, the Grenade Launcher, actually outshines the other two. Despite this, it's worth getting at least one point in Heavy Weapons just for the Grenade Launcher, as it's fantastic for clearing out large groups of enemies and the stronger foes you'll face in the late game, and it's also extremely versatile due to its variety of ammo types. Even when only using the Grenade Launcher, it can be worth boosting your Heavy Weapons to 6 solely for the damage bonuses you'll get.

Exotic Weapons

Governs: Crystal Shard, Viral Proliferator, Annelid Launcher Maximum value: 6 Evaluation: Exotic Weapons are a love it or hate it affair - while the Crystal Shard is the most powerful melee weapon in the game, the two other Exotics are of a more questionable use, especially due to how late in the game they come, and how rare their ammunition is, not to mention the generally high requirements for the weapons and the fact that they all must be researched before use. Like Energy Weapons, Exotic Weapons are specialised against a certain enemy, though in this case it's the various Annelids you'll face, but given the number of them compared to mechs, Exotic is probably the better choice of the two, even though you'll only get to reap the rewards once you get to the Rickenbacker and Body of the Many. The main exception is the Crystal Shard - if you're going pure melee, bringing Exotic up to 6 to get the maximum damage out of the Crystal Shard is a very worthy investment.