Well there's a nice cop-out answer that you are already aware of that is different things work well in some ways and not others.
I'll comment about the Brawl/GH example you brought up. For Brawl, I think the issue wasn't really "you need to play a bit to unlock some characters" but it was "you need to play a lot of the campaign to unlock the characters you've been making a big deal about being included and that everyone is going to want try out asap." For Guitar Hero, well... at this point you can't really win, since most (opinion) people who are going to keep buying RB/GH installments are already good enough to jump right to the harder stuff, but it will take away the fun of unlocking new stuff. But um... okay well the stuff I said about Brawl is still there.
I'll comment about the Brawl/GH example you brought up. For Brawl, I think the issue wasn't really "you need to play a bit to unlock some characters" but it was "you need to play a lot of the campaign to unlock the characters you've been making a big deal about being included and that everyone is going to want try out asap." For Guitar Hero, well... at this point you can't really win, since most (opinion) people who are going to keep buying RB/GH installments are already good enough to jump right to the harder stuff, but it will take away the fun of unlocking new stuff. But um... okay well the stuff I said about Brawl is still there.
