I like it quite a bit. The first three seasons seem almost like a different show. When you get into the fourth season the pacing picksup quite a bit and the scifi elements really come to the forefront. It is complicated and the character flashbacks do get a bit tedious at times, but overall it certainly was a great show.
I think it's greatest strength is that it was truly a character driven show and not just a show about a bunch of strangers stranded on a mysterious island. Most of the show seemed to come from the characters and not the situations. Good writing.
"Death, delicious strawberry flavored death!"