I know this is a tricky question and not too many movies can actually get better with re-watch.
But are there some which meet this criterion?
For me:
1. Piku
2. Wake Up Sid
3. Omkara
4. Dil Chahta hai
Piku and Wake Up Sid I can watch umpteen times and not get bored. In fact, I love these 2 movies so much I always seem to discover something new and they make me feel wonderful.
Omkara because of the performances, especially Saif's brilliant performance. I just feel like watching it because Saif's performance just seems to get edgier and better with each watch. I'm not even kidding when I say I equate Omkara with Langda Tyagi.
Dil Chahta Hai, of course, is as timeless as bread and butter. It's just so frothy and funny and charming. Every scene is worth watching.
Which movies do you feel get better with re-watching or at least you can watch umpteen times without getting bored?
Pinjar. I didn't like the Urmila-Manoj Bajpai pairing at the time and I was too young to appreciate "all" the nuances. Like her hating him to the extent of being glad when she miscarried, her longing for a child later etc. It is haunting and the casting makes perfect sense now because Urmila's husband had to be rustic with a rough exterior and a tender heart. Manoj portrays it beautifully. Her life post-marriage had to be totally different from what she was used to before.
There are many for me but one I watched recently again and still loved so much was Talaash. That movie gives me goosebumps still and is so creepy. The music is so good too.
Talaash gets significantly better the second time when you are no longer involved and subsequently disappointed by the whodunit aspect of it.