In Mass Effect 2, some weapons did more damage to a certain type of defence (shields, barriers or armour). Is the same true in Mass Effect 3?
Yes, it would appear it works like it did in ME2. It might not be right to say "they do more damage" since it's not clear that they get an actual damage bonus, but rather that they are more effective due to the way the barrier/shield/armor mechanics work.
- Rapid fire weapons are good against shields and barriers.
- Slower-firing weapons that do heavy damage are good against armor.
It's not the same. Weapons no longer have percent bonuses. Instead, armor (and only armor) reduces the damage of each hit by a fixed amount depending on difficulty (50 on Insanity/gold, less on lower difficulties). This makes it so low damage weapons are significantly worse against armor than high-damage weapons. In general, the rapid-fire weapons have low damage, and slow-fire weapons have high damage (with the exception of shotguns, which have a low fire rate, but fire multiple low damage pellets per shot).