The DVDs refer to the specific season. You won't get Season 2 spoilers on a Season 1 disc.

I've watched the first four seasons of LOST. Overall I like it even though it's annoyingly cryptic for no real reason. You just want to shake the characters and force them to spit out whatever little secret they are holding.

From what I've seen the show is pretty consistent. If you like the first four episodes you'll like the rest. For what it's worth, I think the seasons are too long (I like the cable/BBC 9-13 episode seasons) and I don't really like any of the characters so my enjoyment consists of the various plot points/mysteries.