Lost was great. Yeah the finale was shit but people get too caught up in one episode out of over 100. It was a great show.
Most shows that are both good and successful have their ups and downs. People here adore the Wire but the last season of that as terrible too and season 2 is horribly paced. The Shield is another one that had a good few pointless, meandering seasons. Lost goes in the same bracket as those shows for me. Great shows but slightly flawed.
Not everything can be as brilliant as The Sopranos and Breaking Bad.