If I was a struggling or mid range sf author I'd probably be very annoyed with Audrey Niffenegger, how dare she write a romantic first novel using a popular sf trope and sell them on mainstream shelves by the truck load? Fortunately I am not an author of any kind so I feel more forgiving. I think she dared because she has a very good story to tell and knows she is capable of telling it effectively. My only annoyance with this book is that it is not marketed as sf when it clearly is sf even though the emphasis is not on the sf side of it. I am also annoyed that since the commercial success of this novel Ms. Niffenegger has not decided to pursue a career as an sf author. This novel shows that she belongs to this genre. She even coins a very sf-ish term "chrono-impaired" for the protagonist Henry DeTamble's involuntary time travelling condition, how "sci-fi" is that? Of course since this book is not hard sf no rhyme or reason is given for Henry's uncontrollable time traveling. He just does it OK? It is no more unbelievable than FTL travel through hyperspace or teleportation. That said, the time traveling element is very well done, I personally can not find any illogical paradoxes that can bring the whole story down like a house of cards. I don't suppose the internal logic of the story is entirely water-tight, more observant or analytical sf readers than myself will probably find some logical fallacies to grumble about, but it is smooth enough for me.
Given that time travel is not the point of this novel the characterization need to be the priority for the author. Both the lead characters are likable and believable, their romantic relationship which is the heart of this book is suitably poignant, and the pathos at the end is rightly emotional. At no time did I cry like a little girl but the corners of my mouth did droop a little bit, and I finished the book with a warm and tingly feeling.
So yes, a solid recommendation for anyone who likes a good time travel story with a touch (well, a massive heap) of romance.