Brain was boring anyway. They've done every story imaginable with him. Even the Brian and Stewie roadtrips were becoming stale. I always found Brian as a character to be fairly unlikeable, and it was intentional to make him look like a massive douche. He wasn't even that funny really, he really only ever echoed the funny things Stewie said, and set up cutaways.
I like that they were ballsy enough to shake the series up (because people HAVE been saying Family Guy is getting worse, which I disagree with). And I actually like the dynamic Vinnie brings to the show as being Stewies protector, rather than Brian who just went along with Stewies schemes. according to the writers, Vinnie doesn't take any of Stewies bullpomegranate, and calls him out on the bad things he does, so it will be interesting to see 2 characters who clearly like each other come into conflict.
I find it ridiculous that people are saying they dislike Vinnie already and that he is nowhere near as good as Brian. He was there for like half an episode, and had a serious part to play in that episode too. I think people should give it a chance, rather than this kneejerk reaction i'm seeing all over the internet of "they killed the show!", and that godawful petition to bring Brian back.
People have literally stated that they are no longer going to watch the show after this episode. Which I think is stupid, they aren't giving the new character a chance. So yeah, watch the ratings fall and one of the best shows on TV be cancelled again because people are too stupid to accept change. I hate the internet sometimes.