It was a VERY interesting episode. We got the door closed on a LOT of mysteries--while opening plenty of new questions.
Answers we got:
1) The button DOES SOMETHING, ALL RIGHT! Holy shit! Locke was WRONG!
2) We know now why the plane crashed! Nothing coincidental about it!
3) What one snowman said to the other snowman.
Questions that got opened:
1) Is Henry Gale "Him"?
2) Where's Michael headed? Is he really chugging off to freedom, or will he redeem himself somehow? Or is he headed back to the beach camp? Or looping around to catch the Others by surprise?
3) "We're the good guys!"... You know, I think they might just be!
4) What happened in the Hatch? Are Locke, Eko and Desmond OK?
5) What's Kelvin's story? How'd he get to the Island?
6) Why did the blacklight come on when Locke was under the blast door? Kelvin (and his predecessor) must have known about the blacklight, yet their faked lockdowns didn't trigger it, and they painted the doormap without it, but knew that the blacklight would make it visible.
7) What's up with the "door" hatch in Yurtville? Is it a fake? Or is it sealed off? Why did the Others have it under armed guard?
8) What's up with the Russians and with Penny Widmore? Is she looking for the island too?
Also--Widmore has come up before. There is a theory that Old Man Widmore's company built the hatches. According to one of the Lost Experience sites, Widmore Labs supplies all the food for the Dharma Initiative. Sun's preganacy test was made by them. See
http://www.widmorelaboratories.com.
EDIT! CORRECTION--those guys in the snow were speaking Portugese, not Russian!