I loved Season 1, when Lost was more about the characters but still mysterious. Season 2 is good too but I felt the hatch and the button kinda overtook everything after awhile. Although I'm curious about the mystery of the island, I care more about the characters. I miss Boone and Shannon. I did love the introduction of Mr. Eko and Desmond (and Libby to a slightly lesser extent) in Season 2 though.
Plus, Season 1 had the HOT Skate kiss and so far, nothing tops that.