A few details I liked about the later 12 Angry Men, just as examples:

-The raving bigot, in the new version, isn't as intimidated by the others' rejection, and eventually changes his vote just to get it over with.
In the old, he starts begging and stuttering, and then proceeds to sit in a chair, shocked. Seems rather impressed by the following arguments, too.

There's much less satisfaction and payoff in the new version - it's not some old bitter man who got put in his place and will probably go home to rethink his life; it's a loud-mouthed (apparently religious) dude in his prime, and from the looks of it, he'll remain a bigot for a long time after that.

-Before the final testimony is deconstructed (the one with the glasses), the new version also has Jack Lemmon looking all intimidated and uncertain when challenged to rebut this testimony, until the old dude comes up with the glasses argument.
This is just to further stress that the weakness of the main character, and the fact that he, indeed, also tried to pull over the jury with some unfinished ideas, hoping to reach a consensus.

So there, just a few details, but totally worth it.

I realize it's all based on a play, but hey, let me ask you:
What difference does it make (I'm now going all "Juror with grudge at his son" here ;) - if the play already got adapted into the movie, is it really any more justified to yet do ANOTHER adaptation, also in a movie, than doing a remake of a movie that wasn't based on a play?

The characters and dialogue are very similar, it might as well have been a remake.

On a side note, they're gonna make another version with George Cloomy and... Sacha Baron Cohen!! God, am I dying to see that :DDD