I admittedly love JGL, but I liked Don Jon a lot. A lot of good laughs in it, and it had some deeper themes and wasn't all in your face about it, which I liked.
This is what I wrote about the ending back when I saw it a few months ago:
Spoiler
I expect that a lot of people won't like the ending, but while the romantic interest in the second half of the movie is predictable, I really liked how they didn't end the movie with them getting engaged and getting married and all that stuff. I like how they ended it as a kinda-sorta couple that is just having fun with each other for now, because to me, it kinda shows that Jon (JGL's character) is finally comfortable with himself and finally knows what he wants/doesn't want to race into anything.
Regarding the "point" of the movie, I thought there were two main points.
1. He was subtly trying to point out that some men need to stop viewing women as things rather than people (like the line when JGL and Barbara went on their first date and JGL said something along the lines of "You're the most beautiful THING I've ever seen in my life").
2. He was trying to point out that a lot of men and women view relationships through a lens. Some men watch porn and end up subconsciously thinking that their relationship should be similar to that (in terms of both the sexual relations and the way that men treat women as things). At the same time, some women watch those romance films (where Barbara took JGL early in the relationship) and eat it up and basically compare their relationships to the relationships they see in romance films. So basically, they think their man needs to be a knight in shining armor. JGL's point is that both of these are unfair. That people shouldn't compare their relationships to anything, and that they should do what makes them feel comfortable, hence the ending where JGL and Esther sort of accept each other (JGL trying to comfort her about the loss of her loved ones if I remember, and Esther not having a problem with him watching porn, but also helping him to move on from it a little bit so that it isn't an actual addiction).
I think there was one other point that I found to be important about the film, but I can't really remember it now. But anyways, I thought it was pretty good.