*Warning Spoilers*!!!!!
For me
Season 1: Was the best, the crash, the monster, the voices, the others, the black rock and than ended with a BANG... the hatch!
Season 2: Was the worse for me... the beginning with the mystery hatch was ok... but when we moved to the tail part of the story (where they began from day 1 again) it suddenly became more and more boring... they were only making more and more questions without answers and they "forced" us to believe all the mystery was the "others" doing, some kind of "cave men" that knew everything.
Season 3: Was not so much better than season 2 at start... again we began from day 1... but now from the view of the others! It was a little WTF! when you saw how they lived. But then again we were going in circles with no answers. Near the end we began to see who was Dharma, but just a lilbit...
We didn't get ANY answers... the monster, the voices, the monster, the numbers, the incident (why you need to press button on hatch). They raised even more questions! I pretty much gave up here... ALMOST!!
Season 4: Now began the flashforwards, which actually answer stuff no one asked... like how many left the island... blablabla... I wanted to know the how and whys!!! They promised!!! They said logical and scientific explanations (like Tekka said). What we get instead? More people on the island... some war between the others and a dude. And those that left wanna go back to island!
More questions? you bet!
Any answers? hell no!
Season 5: Now we would get answers!!! Think again! Instead this time we are trapped in a time travel situations which leds to more confusion and questions... and less answers
We get more info on Dharma... and suddenly... divine "creatures" comes into play... which just through the logical out the windows.
Season 6: Now we are trapped in alternative dimensions/universe... which just brings the question: WHY!?
Also we get the answer on the GODS!!! and the smoke monster... in an indirekt... yet weird way, cuz now it is something else... which brings us new questions.
But basically the series have pretty much come a LONG way from season 1... and simply ignore to answer many simple stuff... like why push button each 108 min in the hatch!? why the tubes from that watch hatch come out nowhere. and so on...
Atleast we have got more answers... what the numbers are (but not why so powerful.. like to win a lottery). The 4 toe statue. The black rock!
Darn... my rant went little to long >.<