Some people claim that Frost wrote the poem "The Road Not Taken" to make fun of his friend Edward Thomas, who had trouble deciding where to go when...

I'm not going to lie, I think you have a tough job ahead of you.  Criticizing Frost's poem in regard to form and structure is going to be tough.  Stylistically, it fits with his other stuff.  It's short, accessible, to the point, and speaks about universal truths.  Also, the rhythm, meter, and rhyme are solid.  

Expressing anger about the poem itself is possible, but not readily apparent.  If Thomas did indeed take a long...

I'm not going to lie, I think you have a tough job ahead of you.  Criticizing Frost's poem in regard to form and structure is going to be tough.  Stylistically, it fits with his other stuff.  It's short, accessible, to the point, and speaks about universal truths.  Also, the rhythm, meter, and rhyme are solid.  

Expressing anger about the poem itself is possible, but not readily apparent.  If Thomas did indeed take a long time to decide which way to go, then the poem supports his attitude.  If a single choice can make all of the difference, it makes sense that Thomas would be diligent about weighing his options.

Perhaps you could have Thomas read the poem and interpret it differently.  He could interpret that making a choice doesn't really matter, because whatever the choice is will still make all of the difference.  He could be angry with Frost for making the decision making process appear to be so flippant and unimportant.  Thomas could also be angry that Frost would be so bold as to equate life changing decisions to picking between two walking trails.  Lastly, Thomas could be angry with Frost for suggesting that once a decision is made it can't be undone.