I have to say, in five years of LOST season premieres, last night's was my favorite. I think what I really liked about it was that for the first time we're really starting to get answers about the island and what's happening on it. I feel like we just got to the top of the first giant hill on a roller coaster, crested the top, and went speeding down into the part where all the fun happens.
Which is not to say there haven't been many important and memorable events so far. But I think by the time season six ends and we pull into the station, we will look back and say that the last two seasons are what really made the show great.
I really want to go into more detail, but I don't want to spoil it for anyone who hasn't seen it yet. Just know that it's not too late: you can still go rent or buy the first four seasons. I'm telling you, this is one of the greatest shows that has ever been or is likely to be.