1988 Catchers must wear protective helmets while on defense.
Good

2008 MLB adds limited (home run calls, fair or foul) instant replay to be in effect for all games starting on Friday, August 29th.
Okay

2014 Runner attempting to score may not deviate from his direct pathway to the plate in order to initiate contact with the catcher (or other player covering home plate). Catcher cannot block plate without possession of ball.
Good

2016 Slides on potential double plays will require that base runners must make a bona fide attempt to reach and remain on base.
Good

2017 Pitchers no longer required to throw four intentional balls to walk a batter. Manager may now ask the plate umpire to let the batter go to first base.
Dumb

2020 Pitcher must face a minimum of three batters in an appearance or pitch to the end of a half-inning.
Neutral.

Temporary / COVID-19 Pandemic Rules Added for Shortened Season:
Extra-inning runner on second base automatically.
Seven-inning doubleheaders.
The postseason expands to 16 teams.
Universal designated hitter.
All dumb

2022 Draft lottery implemented to discourage tanking.
Good

The National League officialy adopts the designated hitter.
Bad

The postseason expands to 12 teams.
Bad

2023 Bases increase in size from 15 to 18 inches.
Bad

Defensive shifts are banned.
Bad

Extra-inning runner on second base, from 2020 temporary rules, made permanent.
Bad

Pitch clocks will be used.
Real Bad

Pitchers are allowed two disengagements per plate appearance without penalty.
Don't care