To understand the problem of this episode, you have to understand how shows like this work.
Basically, you have two choices - you can either tell an interesting story, or you can tell an old and predictable story in a funny way.
The story here - 'get rich, annoy friends, lose friends, blow money, find out friends will forgive you' - is a very old story, so MacFarlane would now have to go with the second option. But he doesn't. Nothing Peter does is really all that funny, and the other characters pretty much don't appear in this episode, which is covered by Lois mentioning each of them in one sentence.
There is so much potential here. Just imagine - Stewie getting his hand on big money - the possibilities are endless. But no.
MacFarlane really seems to think that the story itself is interesting enough to carry this episode.