|For me, part of the problem is that I don't think that "Words Fail" is really a satisfying apology (or a satisfying song, period), and it centers much more on himself than on the people he's hurt. Now, it may be written that way on purpose, but it certainly feeds that sense of ambiguity.
The song also has a problem that I feel a good deal of contemporary musical theatre writing has, unfortunately - it's way too verbose. The song rambles on and on and on, even as Evan claims that "words fail." It becomes a "more is less" kind of song rather quickly, and his attempts to explain just get weaker and weaker. The end of the song, which cleverly tries to link back to "Waving Through A Window," really goes for naught, because too much has been said already and there's no build to that sense of connection or discovery one often gets when hearing a song lead to a reprise quote such as that.