The series begins with a thirty-something Jewish woman who is at a troubled part of her life when she has an allergic reaction that leads her to meet the mysterious "Dr. Tom" at the hospital. We learn more about Tom and others in her life (family, friends and colleagues having various dramas that often, imho, are the best parts of the show; generally, very well acted by the ensemble cast) as things develop. Turns out Dr. Tom is not your average sort of therapist, unless they can control time and space. This allows Erica to be sent back to various "regrets," beginning with going back to a high school dance, while also learning more insights about her life and loved ones.
These, along with the episodes as a whole, tend to be a mixed bag, but overall, the show has enough good material to make it rewarding overall. The charm of DVD is that one can ff through some slow parts. After regular -- so to speak -- therapy, Erica has group therapy in the third season. She meets a new love interest (someone else the focus of earlier episodes*) in group, but it's unfortunate that more effort was not given to understand the others. The fourth season has various characters (including the mom in a very good episode) to have major life developments, Erica herself preparing to be a full fledged doctor while also running a new publishing business with a former supervisor.
A major thing fans of the show wondered about was the "secret" to what was going on. For instance, was she really in a coma (shock from the allergic reaction) or even dead? We saw Erica go into the future and in S4, she met her future self (apparently, Back to the Future rules didn't apply; she also did not understand the concept of separate time lines, the movie not cited for the concept). S4 also informed us about the winner of the World Cup in a few years ... we saw such information could lead to problems in that movie too. But, no big reveals were really shown as late as the penultimate episode, including who was ultimately in control.
And, the show ends without us knowing the details, a sense of incompleteness that fits into its various philosophical moments.
---
* The show at times had a sort of Lifetime or chick flick feel to it with her needing to decide what guy is right for her and so forth. The actress could be a bit too cutesy at times -- for instance, S4 has her repeatedly enthusiastically assuming the wrong thing as a therapist in training -- but I liked her as a whole. The role is pretty prime, especially with all the permutations involved with the time travel and all. As noted in the link, her Jewishness comes out in various cases, her dad in particular.