Some of my favourite films only became so after a few viewings. these include:
An American Werewolf In London: First seen in South Africa (where I grew up) and it was cut to ribbons, thanks to stringent censorship laws
The Thing: John Carpenters classic claustrophobic horror still gets better with each viewing
Kiss Kiss Bang Bang: Shane Black's hugely underestimated and under-appreciated comedy/noir/thriller
S.F.W.: First time I saw this I was very stoned and I thought it was a riot but otherwise forgettable. After the second viewing a year or so later I was able to appreciate the subtlety of Stephen Dorff's performance.
There are loads more but that'll do for now.