You're seeing this discrepancy because star systems are not consistent between critics. For critics like Roger Ebert, 2.5 stars or lower out of 4 stars is always negative. For other critics, 2.5 stars can either be positive or negative.
Also, there's always the possibility of the webmaster or critic putting the wrong rating on a review. If you think this is the case, feel free to email us to argue your case.