Wow, grats on your DJ Hero platinum! That took some doing and dedication. Hopefully it wasn't too much of a grind!
I'm working on Warhammer 40,000: Space Marine now, but am not sure if the platinum is worth the time. You have to get over 7,000 kills online, and thousands of those are with very specific criteria (headshots, multi-kills, fully charged plasma shots, etc.) It is kind of a pain, and the fun factor the game had at first is starting to wear thin. If you're ever boosting Space Marine, pls let me know! Cheers!