A simple - butbynomeans complete, consistent, sound, satisfying, useful, or repeatable - test for good art is whether or not you get something interesting out of it. Beckett's good old absurd and minimal vagueness usually does the trick for me (as it is bent to do?), and Worstward Ho is no exception. Now for that over-quoted excerpt:

All of old. Nothing else ever. Ever tried. Ever failed. No matter. Try again. Fail again. Fail better.

For this kind of thing, I think enjoy it less as a puzzle about meaning and more as trying to merge with its stream of consciousness. That rules me out from being a critic, I guess.