Is The Road Not Taken in some way ironic?
Yes, definitely. The first irony lies in the title. Although the poem's title is The Road Not Taken, the primary focus is on the road that the speaker actually took. One would assume that the speaker would have focused on the subject of the title, but he ironically chooses not to do so. This is clear from the following lines:
Then took the other, as just as fair,And having perhaps the better claim,Because it was grassy and wanted wear;Though as for that the passing thereHad worn them really about the same,I took the one less traveled by,
Oh, I kept the first for another day!
Robert Frost obviously had much fun in composing this poem, for, as he himself reportedly said, the poem is very 'tricky'.
The idea of the poem being 'tricky', has resulted in a great many contrasting interpretations, and herein lies an even greater irony, for the poem is to be understood as a metaphor for choice and whether its outcome is pleasing or not. However, many interpreters deem the poem to be a metaphor for being 'different', not following the crowd. Such interpretations see the narrative as a symbol for those who do not follow the ordinary or mundane and, by making such a choice, also make a difference, not only in their own lives, but also in others'.
In this sense, the poem acquires an inspirational quality, which is not bad at all, but it basically misses the point. The reason for this interpretation is derived from the line:
I took the one less traveled by,And that has made all the difference.
Then took the other, as just as fair,Had worn them really about the same,
...having perhaps the better claim,Because it was grassy and wanted wear;
And that has made all the difference.