About the best thing you can say for the baby Reaper is that it wasn't as disgraceful as the baby Alien from Alien: Resurrection. Yes, both creatures were grotesque fusions of human and eldritch alien killing machine that served as foul effigies of mankind, but at least the Reaper didn't call Shepard "mama" and single-handedly undermine the ineffable horror of one of cinema's most iconic monsters. Small favors and all that.
In light of how absolutely tepid its final boss encounter turned out to be, that fact that it ultimately didn't ruin the game speaks a lot for ME2's quality. Although the boss itself made a poor climax for a mission around which the entire game was structured, the reward was in the mission itself. By focusing on the dynamics of the team the player had assembled and strengthened over the course of 30-40 hours of play, the final battle made use of the full RPG party in a way no other role-playing game has ever accomplished. ME2's final assault on the Reaper base drew obvious inspiration from The Dirty Dozen, but it reworked that concept into something wholly unique and intensely satisfying. Only players who had taken the time to invest themselves into their team and come to know their comrades' capabilities could survive the final encounter, let alone hope to come home with no casualties.