Here's a quick summary for anyone who is not familiar with the Mass Effect series. Mass Effect is a 3 part RPG shooter series of blockbuster video games developed by Bioware, which is owned by Electronic Arts. The first 2 games were very popular and loved by fans. The 3rd and final game was recently released. The majority of the story and gameplay were well received by pretty much everyone, but many fans of the series are upset about how the game ended. There's almost universal disappointment on on-line forums (though people who liked it are probably less vocal). A couple of complaints are

1. Despite the series being based on players being able to make different choices that affect the story, almost nothing the player does throughout the series affects the ending.

2. Although players have a choice of 3 different options during the ending affecting the fate of the galaxy, the only thing that changes in the following cutscenes is the color of some explosions (green for one choice, red for another, blue for the last)

3. The ending felt like a deus ex machina and wasn't satisfying

Lots of fans have expressed their criticism on-line, with many hoping that Bioware will "fix" the ending or release a DLC that alters or extends the ending. This is Bioware's first response as far as I know.