What one rule would you change and why? I'm thinking of the core ruleset, but if something really bothers you about a rule in a Codex, you can list that too. This topic comes up every now and again, but now that we're a bit deeper into 6th Edition (and now that we've seen a good number of 6th Edition codices), it seems more relevant.

There are a few things that are annoying about 6th, but my single change is:

If a unit is falling back or pinned, it cannot fire overwatch. This is a pretty simple change, but it makes the penalty for being pinned or falling back a bit more severe. Plus, it adds an interesting tactical element of trying to pin or break units in preparation for a charge.

What else is out there that you would change?