He kind of lacks a certain "it factor", compared to various alternatives like Newsom, Whitmer, Shapiro, Moore, Polis, Beshear or even Pritzker. He's just too much of a Generic D and sort of bland. I could see him as a solid, do-no-harm VP candidate to Harris though.
Not to nitpick but I'd say Pritzker - billionaire businessman who bought the seat and has been a generic D rubber stamp - definitely lacks the it factor, and so might Shapiro, much as I like him.
Could be very wrong in my reservations about Shapiro (and I'll happily eat crow if so) but Pritzker is most certainly not it. He honestly wouldn't fare much better than Bloomberg.