FWIW I never found my HD600 or 650 all that detail retrieving or revealing. I hear more "stuff" with my RS1 and K701. But thats what I like about the senns... particularly the HD650 its a very smooth, soothing headphone to listen to. In terms of detail reveal-abilities the 650 is right in the middle of the pack in my collection.
When I think fun and forgiving... thats the Grado SR sound. Pick one in your price range. The 60 and 225 I think are the sweet spots in the SR lineup.
I agree that the Grado sound is lots of fun, but I wouldn't characterize it as "forgiving"
(...and I love my SR225i's).
"Fun and forgiving" headphones, per the OP:
+1 on the Philips X1.