Decent watch at best, could watch again, and can recommend.
I'm a fan of Matt Damon, but not so much Greg Kinnear, though both are clearly quality actors. This movie is extremely charming, and very well written and produced. It is obvious that they knew they had a contentious concept and needed to create something that deals with it carefully and tastefully.
As an idea that, "oh, they can't get away from each other!" is funny short term, like if they were glued together on accident ("Family Guy"), but as the sadness of the reality sets in they try to compete with overly ridiculous scenarios that wouldn't happen in real life and try to swing the odd situations as beneficial. As that becomes obviously untrue, the sadness of it sets back in and is doubled by the idea of being permanently stuck with someone so wildly different that you.
If you can look past reality, then there is a lot of good humor in here, and a really touching love story crossed with a story of ambition versus family.
Other than funny, this movie feels like it tries to be too many things, but that comes from having two wildly different characters each pursuing their own stories. There's just a lot of overhead.
There are a lot of problems with the movie, but it's uniquely charming, and there just aren't many conjoined twin stories.