You actually get x2 Exp from kills, I'm not sure if you get x2 DP as well, but you might. It's harder to track.
Another difference though is the cost of stamina. On Hard all skills and actions drain a lot more stamina. This means that you can't spam skills/spells the same way. Big spells might drain all your stamina, leaving you winded. It does change your gameplay a little.
Especially for fights where you cling to monsters. On hard, stamina will drain faster, so you won't be able to hold on for as long, especially if they start trying to shake you off.