8 Times DLC Ruined The Base Game

Here's another example of a mediocre DLC which became game-ruiningly bad when it was made a mandatory part of the core experience in a re-release. 

Deus Ex: Human Revolution's The Missing Link DLC is a roughly 4-hour mini-campaign in which Adam Jensen is captured and temporarily stripped of all his weapons and augmentations - a terrifying prospect for players who've spent hours and hours refining their build.

While in Human Revolution's original release this was an entirely optional component of the game, in the 2013 Director's Cut it's baked into the core campaign, ensuring that for players keen to carry on with the main story, it could become an exhausting, deeply irritating and entirely unskippable roadblock.

Given that The Missing Link was originally released as an entirely standalone DLC, retroactively inserting it into the main game was a huge mistake on Eidos Montréal's part, ensuring that an otherwise remarkable Director's Cut - which thankfully remedied the original release's horrendous boss fights - became an abject chore to finish.