Steve Carell is just fine as the cuckolded dad, who's never had to romance a woman in his life. He wears baggy khakis and New Balance sneakers to dinner- I normally would call this "I surrender", but marrying your high school sweetheart means you never had to try in the first place.
Julianne Moore is his wife, who's having a much-deserved midlife crisis after 25 years with her high school sweetheart. Her part is a bit underwritten- there's one scene missing that justifies why she point-blank wants a divorce. She has a fling/affair with colleague Kevin Bacon, just slick and smarmy enough to gross us out.

I simply loved Marisa Tomei as a single lady out for a good time. When Carell completely botches his sloppy attempt at picking her up, some kind of reverse-lock takes effect- the same kind of surprising but organic relationship. Also, when her character finally goes off the rails, it's electric- I remember why she won that Oscar for comedy way back when.
Analeigh Tipton is perfect as the gawky, overdressed teenage girl who has a crush on Carell, but is pursued by Carell's son (Jonah Bobo, perfectly cast as Carell and Moore's offspring)
My wife thought this was based on a French comedy-- the slapstick third act certainly feels like it-- but it's credited to Dan Fogelman, who wrote three animated movies before this (Cars, Bolt, and Tangled) and has since created the aliens-in-my-subdivision TV comedy The Neighbors.
Steve Carell is a comedy genius - under-appreciated for his work on The Office - but his movie choices have been uneven. The Forty-Year-Old Virgin is brilliant, Little Miss Sunshine is very pleasant, but Get Smart, Dan In Real Life, Evan Almighty, Date Night, and Dinner For Schmucks are all lukewarm at best. I also believe that audiences are more reluctant to spend money to see a TV star in a feature film. The thinking goes- "I have seen Carell on The Office for free for six years- why should I pay $12 to see him act goofy in a movie?" This is why I have yet to see a Tina Fey movie in a theater, while I have seen every episode of 30 Rock, many of them twice. The good news for Carell and Fey: our standards our lower for renting a movie on a Friday night.
My wife saw CSL with her lady friends in the summer of 2011. In the summer of 2011, the TV commericals made CSL look like another formulaic rom-com, much like the other two rom coms that year, No Strings Attached and Friends With Benefits. Turns out CSL is a thoughtful, nuanced, intelligent comedy (with a wacky streak) that happily surprised me 18 months later, watching my mother-in-law's Netflix DVD with my wife and sister-in-law.
NOTE: both of those rom-coms co-starred That 70s Show alumni -- Ashton Kutcher in one, and Mila Kunis in the other. At the time, I tweeted:
Every cast member from That 70s Show is doing one. Next up is Topher Grace & Jessica Alba in "Fuckbuddies!"