"Rule: When an appositive is essential to the meaning of the noun it belongs to, don’t use commas. When the noun preceding the appositive provides sufficient identification on its own, use commas around the appositive.
"Example: Jorge Torres, our senator, was born in California.
Explanation: Our senator is an appositive of the proper noun Jorge Torres. Our senator is surrounded by commas because Jorge Torres is a precise identifier" (from here).
- My brother Ken is a minister in the PCA denomination.
- My trainer, Jim Shipshape, is also a bodybuilder.
- Raconteur Ed Schlemiel will be speaking at the Jewish Community Center tonight.
- Mezzo-soprano Hilda Gutenberg is a world-class opera singer.
- Question: Who is coming with you on the canoe trip, and what is his name? Answer: My dad Harold will be accompanying me.
In conclusion, the appositive in your first sentence is George. Does the noun phrase which precedes it provide sufficient identification on its own? The answer is yes. So set off the appositive with commas.
The appositive in your second sentence is "The Road Not Taken." Are the words which precede it (namely, the poem) essential to its meaning? The answer is yes, because Frost wrote many, many poems, but only one of his poems is most famous. Therefore, the poem and "The Road Not Taken" are essential to one another. No commas are needed.