The studio behind hit video game Mass Effect 3 on Monday said fans who wanted a happier ending may get a slice of what they wish for, following an online campaign calling for changes.

The game's executive producer Casey Hudson acknowledged in an online post that the chosen conclusion to the gripping science fiction action trilogy had generated "a lot of discussion and debate," but stood firm on the decision.

Mass Effect 3 ... some gamers are unhappy with the trilogy's ending.

"We always intended that the scale of the conflict and the underlying theme of sacrifice would lead to a bittersweet ending," he explained in the studio's first and only response to the campaign," on gamemaker BioWare's website forum.

"To do otherwise would betray the agonizing decisions Shepard had to make along the way," he continued, in a reference to the heroic character whose choices and actions are controlled by players in all three titles.