Starmer doesn't really do it for me either, but I don't think I'm really the type of voter he's targeting. I'm never going to vote Tory and certainly with this particularly odious brand of Tory I'll vote for anyone who can stop them who isn't right wing. To an extent, he can take my vote for granted. Certainly this time round.
Who he needs to win over are those voters in the centre or even right of centre. He's trying to win an election as opposed to convincing people socialist policies are the good of the country and the majority of people in it.
It's a fine line he's trying to walk, he thinks he needs to be able to convince voters with some very different political beliefs to vote for labour in order to win. Which means he isn't really going to particularly inspire anyone, but hopefully won't turn too many people off labour either. It's clearly annoyed a lot people to the left of the party.
I don't know if that's the right approach or not, but whatever else you think of him, he's clearly no idiot. I think he's hoping that those labour voters who are a bit annoyed, or uninspired when push comes to shove will vote labour anyway to stop Johnson (and/or that the numbers of those really annoyed aren't significant enough anyway) and that he'll also hoover up significant votes from the centre.
It's a fine line, but looks to me like that's his strategy. Easy to judge, but it's a very difficult position to be in. Corbyn was marmite and he needs to bring back voters who (rightly or wrongly) hated him. He needs to show them he's different. He also has a hostile media to contend with who have spent decades brainwashing large parts of the population into thinking socialism - bad.
So even if you don't necessarily like him or agree with him, there is definitely a logic to his approach.