Sorry this took so long but I enjoyed the film quite a lot. Spoilers???:
It's different from the play in a lot of ways (lots of exterior shots, outside of the home, obviously, which means new scenes; multiple scenes with Jason and Becca as opposed to just that major one in the play; new characters, in the form of Sandra Oh's, mainly) and it is affecting in a very different way. While the play, I found to be, effective because of how unsentimentally honest it was, the movie is still pretty honest but definitely more fragile in dealing with the issue, especially towards the end. We get scenes where Becca breaks down crying in her car (but it doesn't feel contrived, which is pretty surprising) and Howie breaks down crying while yelling at Taz, the dog (which also is pretty touching). It doesn't feel heavy-handed and the sentimental stuff does work...it feels very genuine but it's definitely different from the play. The ending montage is fantastic (it still ends the same way pretty much). It's also less funny than the play...but still definitely provides much-needed moments of humor.
I will be the first to admit that Nicole Kidman is excellent. Her face actually moves (kinda)!! She is really stripped down here, giving her best performance in a very, very long time. She deserves an Oscar nod. Aaron Eckhart, who I think is a wildly underrated talent, is every bit Kidman's equal. They have great chemistry. Tammy Blanchard plays Izzy very differently than Mary Catherine Garrison, but is definitely very good. And Diane Wiest is extremely touching as Nat. Again, very different from her stage counterpart, Tyne Daly, and much more introverted and quiet, but she's wonderful.
I think the movie is going to have a very hard time finding an audience. It's nothing extravagant, it's a bare-bones film with an honest heart, some great performances, and it really does get under your skin. The subject matter doesn't help either. But I hope it gets a couple of Oscar nods...it certainly deserves to be recognized.
If anyone has any specific questions, I'd be more than happy to answer!