I've watched it from the start. They have thrown in lots of mysteries and I wanted to see the answers, which weren't provided in the finale. I think after awhile the fans continue to watch because of the characters and the mysteries become less important.
The finale was not what I was thinking it would be, and was a bit of a letdown. However it wasn't nearly as bad as it could have been. I think it was important for the characters to come together and put all of the turmoil behind them, and at least they did that.
My feeling has always been that the creators didn't know how popular the show would be or how long it would run, so once it became a hit then they had to make up story lines and figure out how to make a lot more show out of it than they first had in mind.