Part of why you feel might feel that way is the non-linear way time works in the show. His break comes when he spends one day with a concerned Rita, and with her observation that he's the lucky one since he gets to change--everyone else is stuck being the same. From that point, until the final iteration it must have been thousands of days, even though we only see a few as he becomes more selfless. How do we know--the piano teacher tells us "it takes people thousands of hours to master this", which he does an hour or two in a day by the end.
I also really like the way they use secondary characters. Here Ned Ryerson is no longer just a comic foil as in the movie. He has his own related story (his song - Night will come). In the movie you feel that any rapprochement between Ned and Phil is just an expediency to get Ned to stop bothering him. Here, Ned is a more fully realized sympathetic character
Nancy, and her song, looks like a throwaway, but joins in with the story of Larry who, wearing a shirt that Phil helped him pick out, and that is a perfect reflection of him, picks up Nancy and they seemingly end up dancing for hours (unlike in the movie).
Oh, and as I told Tim at last nights show. Loved the allusion/paraphrase to Resume by Dorothy Parker that Phil recites when listing off his suicide attempts.