If I've never seen The Departed...

This is a tricky one. Usually if people see a film and really like it, any other version is automatically at a disadvantage because not only does it have be better than the first one, but it also has to dislodge the loyalty the first one gained by being liked. Does that make sense?

When you watch a film, you subconsciously grade the characters, some you will like and some you will dislike. Those you like will become honorary virtual friends for the duration of the film, you will be left with a feeling of friendship and allegiance towards them. When you watch a different version of the film, the characters will be played differently and will be seen as trying to usurp your honorary virtual friends from your favour, you will resist this and not like the film as much as a consequence.

If you watch a film, and it is "okay" and "entertaining enough", a different version will have a far easier job of being seen as the better film because the subconscious allegiance you feel towards the first film is far weaker than if you really liked it. Still making sense?

In this case, with Infernal Affairs and The Departed, I saw the original trilogy first and absolutely loved it, so The Departed was already fighting a loosing battle. But, having watched The Departed, I don't think it would have been my favourite of the two even if I'd seen it first. There was too much I didn't like about it, and not just the differences between it and the original. So much so, I feel that I wouldn't have even watched the original if I'd seen The Departed first.

Will your experience of The Departed be killed by seeing Infernal Affairs first? If you are going to like The Departed at all, then I think Infernal Affairs will probably detract from your experience of The Departed, simply because IMHO it does everything better ... especially the ending.

If you watch Infernal Affairs first, it will naturally spoil certain plot points that both films share. The reverse is also true, but for my money, you lose more by having Infernal Affairs spoiled by The Departed.

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http://www.youtube.com/watch?v=0e3tGxnFKfE

http://tinyurl.com/LTROI-story

Well, i've seen The Departed first and just a while ago Infernal affairs. The thing is when i saw The departed i liked it i didn't even knew it was a remake but i liked Infernal affairs too although i would have preferred to see this one first because i'm a fan of asian films and it kind of sucked knowing what will be happening next. But i'm sure the other way can be like this too.
Sorry for my poor english.

It won't kill it but it will be a completely different experience. Coming from someone who saw the Departed first. I will say that I prefer the original Asian version.

One of the movies will spoil the other, it's a remake and some of the most importants plot points and scenes are the same. I recommend watching Ifernal Affairs first, since it's the original movie. After a few months I think you can watch The Departed... Don't watch them in one sit cause they are basically the same movie.