Go back and play Asteroids where the computer ships can mathematically calculate exactly where you are going to be and shoot you out of the...space, because of it.
There's a difference between frustration and difficulty.
IMO, difficulty should be able to be overcome with patience and strategy. 4 snipers being able to blow your head off the second you pop out of cover is not difficult, it's cheap, it's frustrating. Beating frustrating parts doesn't do a thing; it just proves you can get lucky, or that the AI felt sorry for you and let you get by.
ME 2. Some areas of the game will have multiple sections, and each section will have something that will wind up killing you multiple times, until you figure out which areas of cover to use, which biotic powers are most effective, etc. THAT'S Difficult.
Frustrating is also in ME 2. The Mechs rocket you out of cover somehow and then instantly destroy you with their machine gun arm. One side mission where you have to stop 3 of them from destroying boxes took me hundreds of tries, dying many times on the LAST Mech when it was down to just its Health.