disclaimer: While I try not to spoil too much, it is difficult for me to ascertain what the essential plot elements are for others, so I may be giving them away. Also, in this discussion I am, in my mind, assuming that the primary version of the film is the American version, though it was made second as an adaptation of the Italian film.
After wanting to see it for several months, I finally was able to see "l'Ultimo Bacio" on Wednesday night. I saw the American version, "The Last Kiss" featuring Zach Braff, in theaters and have watched the DVD several times since its release. I didn't really anticipate liking the Italian original more, and I was right. I've not watched too many Italian films, save for "La Vita è bella" and a few different operas, but I was expecting this movie to be highly sexually charged. The American version was uncomfortable sexual tension at times, and with my impression of Italians as overtly sexual (they recently passed a law banning crotch grabbing in public), I expected even more tension. It's not that I was disappointed by the lack of graphic material (on the contrary, it was a pleasant surprise because it's always awkward) but I believe it lacked some of the essential elements (at least for me) that the American version so deftly added.
While not equally so, "The Last Kiss" is similar in tension to "Closer." I've never felt more awkward/amazed as I did after watching "Closer," and "The Last Kiss" maintains many of the same elements of tension, struggle, and pain. "l'Ultimo Bacio" lacks that tension, but it still tells a good story very well and the acting is good, though it's hard for me to judge non-English speaking actors because I'm just not familiar with the natural inflection.
The Italian film developed many of the side stories better, and while that provides a deeper picture of the periphery actors, I believe it takes away from the primary quintet of characters: man, woman, mom, dad, and girl. There is a significant difference in the endings and it sharply paints one of the characters in a different light. That's all I'm going to say about it, perhaps I've said too much already.