There are a number issues here:
- Is this really a constitutional decision or does it step on the toes of the states? This is a case where the federal government tells the states how to apportion their legislatures. It's based on the equal protection clause of the 14th Amendment. But does that truly give the federal government the power to meddle in this area?
- The case ignores traditional political divisions. In other words, you no longer have a representative who represents County X (a traditional political unit). Instead, that person might represent a couple different counties (in sparsely populated areas like where I live).
- The representatives might not represent coherent communities. If they have to represent set numbers of people they might have to represent groups of very different people instead of homogeneous groups.
- It has led to lots of gerrymandering where districts are drawn for political gain (instead of just having traditional divisons -- you represent County X, you represent Town Y, etc).