Star Trek: Enterprise
Star Trek: Enterprise (often abbreviated ENT) is a roundly panned series that was cancelled after just four seasons instead of being allowed to achieve the "traditional" seven seasons that every Star Trek show has done since Star Trek: The Next Generation.
Continuity? What Continuity?
Another point of criticism was that the writers did not follow long-established Trek canon; instead making up history as they went along, often using contrived scenarios to justify introducing characters and concepts that had no place in a prequel.
Token Black Guy
Ensign Travis Mayweather soon became the series' Token Black Guy; he frequently failed to appear in episodes, and when he did, it was often to say a single line or just lurk in the background.
The Temporal Cold War
The Temporal Cold War was a recurring plotline about unspecified future people trying to alter history by messing with the past. The plot thread never really went anywhere, and -- damningly -- not even the writers knew how this plotline would be resolved.
Starting from the late third season, the show's quality began to improve, mainly thanks to a new producer and changes in the writing staff. The fourth season is generally regarded as the show's best effort at living up to it's premise, garnering praise from both the fans and professional reviewers.