Allison Janney is really really good in Mom, and I would normally say that she's the person carrying the show, but I can't go that far - everyone else is good too, especially Faris.
It's just a solid B/B+ overall, and not just for a multi-cam, but for a comedy in general.
It's funny, but unafraid of real emotions and real moments, especially to do with the two main character's sobriety (it's basically about Janney and Faris being a mother and a daughter and being parents as well as recovering alcoholics/drug addicts).
I know you watch TBBT, so if you can sit through it and enjoy it (like me) I think you'll find this about 2 or 3 levels above in terms of quality, writing, jokes and story.
It's just a good show that has gotten better from an already good 1st 2 seasons.