Several research firms spent a considerable fortune trying to redesign the Widow sniper rifle. Their goal was to retain the geth weapon's considerable firepower while reducing its recoil, so that the gun could be fired without breaking a nonsynthetic's arm. After much trial and error, one company finally produced a usable model rolled out to the galactic market.
The Widow is one of three sniper rifles in multiplayer capable of armor piercing without the aid of Armor-Piercing Ammo or the use of a piercing mod. It has a native 50cm penetration rate, which is enough to pierce most thin cover. With the piercing mod added on the Widow, the penetration distance gets even larger, but that won't increase the damage done to enemies after passing through objects.
The Widow cripples players who want to use powers frequently. Even if a player is using a level X on its own with weight-reduction evolutions and without a second weapon, it is still heavy. Soldiers that do not rely on their powers may find the Widow more useful. Other classes and races may have weight problems with it and should be mindful of the extra cooldown time on powers and abilities.
Ammunition for the Widow, even at level X, is still even more scant than the Mantis, and using a Spare Capacity mod will benefit the Widow greatly. It can be combined with the High Velocity Barrel to maintain damage and penetration without losing out on ammunition, but it isn't as effective as having two anti-armor/cover mods.
Shot for shot, the Widow will do more damage than the Valiant, Mantis, Black Widow, and Krysae, but has the obvious disadvantage of having to reload after each shot. Because of the nature of this weapon, it is deadlier than the mentioned weapons, and hits immediately, unlike the Krysae or Kishock, but will do less damage than the Javelin and Kishock. It is very effective against infantry that are lined up, or armored units like Brutes or Dragoons, but reload time needs to be taken into consideration. The reload time can be reduced through reload cancelling, though this still takes several seconds.
Adrenaline Rush will drastically improve the effectiveness of the Widow through the 50-70% damage bonus it receives. You can get at least 2 shots off upon activation, or 4 with reload cancelling, which can shred through armor. Tactical Cloak is not as effective in terms of duration, but it gains a bigger damage bonus (up to 80%) for the next shot.
Because of the damage of the Widow, aiming for the head is not necessary for taking down unshielded foes on lower difficulties.