The intent is to eliminate gerrymandering, of course. The problem with the law might be that the Constitution (Article I, Section 4) states:
The times, places and manner of holding elections for Senators and Representatives, shall be prescribed in each state by the legislature thereof ...I am torn on this question on both ideological and pragmatic grounds.
On one ideological hand, I am a hard-core federalist, and believe that 'the laboratory of the states' is the best way to test ideas; on the other hand, as a believer in rather literal interpretations of the Constitution, I think 'the legislature' means, you know, the legislature.
Pragmatically, I detest gerrymandering and would be happy to see more competitive districts open up. On the other hand, I doubt whether in practice most 'non-partisan' commissions will end up being actually non-partisan (Arizona Republicans think the Democrats gamed the system this time. They may be right, but I don't think for an instant that Republicans are above doing the same).
There's another area in which my beliefs are in conflict on this case, though less so than in the examples above. I'm a strong believer in direct democracy where feasible -- i.e., citizens passing laws, as they did in this case, through referenda. However, I don't think citizens have any more right than a legislature to act unconstitutionally, so that concern really doesn't enter into this.
In addition to Arizona, several other states, including California, have redistricting commissions, so the decision may have wide ramifications.