I've always been interested in having a good understanding of Gentzen's proof of the consistency of arithmetic.
Being more precise, he showed that $PRA + WF(\epsilon_0) \vdash Con(PA)$.
I am interested in an exposition of his work that
1) Is transparent on which parts of the consistency proof uses the well-foundness of $\epsilon_0$.
2) Discuss (in mathematical and philosphical way) to what extent this proof deviate from the original Hilbert's Program, and in what extent it fits in a nice way to a more flexible formulation of this programme.
I should also add:
0) Is technically as simple as possible.
Item 0) is because I think this question might be of interest to the curious general mathematician.