Well, don't forget... a) he's a kid b) the only person/people he hates at this point are the Jedi/Mace. I'm sure that once he matures a bit more, destroying a bunch of kids wouldn't bother him a bit, but I guess that since he's still a kid himself, he kinda felt bad.
You know, the toned-down Fett kinda bothered me too, but your explanation makes sense.
That said, I was still not wowed (except for Artoo's antics in delaying the bounty hunters). Basic-speaking Bossk was a bit surprising, but it didn't really bother me. What DID bother me was the apparent destruction of Jango's helmet, the Slave I, and Aurra Sing. Until I hear otherwise, I'm choosing to believe that Sing and the ship survived. Aurra is a decent adversary who could be utilized some more in the next season, but the wanton rewriting of canon really takes a lot away from what we know and love about Boba Fett. There were some opportunities that they could have taken to establish his future character, but they wasted them.
I dunno, man...next season has a lot to make up for.