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I'm a casual Marvel Cinematic Universe (MCU) film fan and have probably watched about a third of the MCU films that came out since Iron Man (2008). Is there a "Critical Path" of MCU films I should watch (or have watched) prior to watching Avengers: Endgame? I know Avengers: Endgame has not yet come out, but I'm hoping that by the time it's released (April 26, 2019 here in the US), I'll have caught up with those movies I've missed to ensure I'm minimizing any plot holes due to missing a prior film.
Side Note: If this question belongs on a different SE site (such as Science Fiction & Fantasy), please feel free to migrate it on my behalf.