Like many people, I somewhat like Jacob but nowhere near as much as other members of the squad (he's probably tied with Miranda for least favorite, or perhaps with Zaeed and Legion as second least). I find him comparatively boring in relation to the others.
Many people have pointed out - with some justification - that, "Oh, so lack of emotional baggage and issues means you're BORING LOL." Which is an attitude I disagree with; I think well balanced, emotionally stable people can make some of the coolest characters around.
I think Jacob's problem is that he lacks a character hook. I'd almost say a "quirk", but more than that. If you asked me who he *is* or what he's like, I'd have a lot harder time nailing it down than any of the other characters. Miranda is frosty and superior, Jack is angry and psychotic, Tali is flustered and adorable, Garrus is snarky but troubled, Mordin loves singing, Samara has a calm air, Grunt likes fighting, etc etc... you can really get a grip on who they are, or what they like, or even some random things like Zaeed's accent and love for his rifle. Jacob doesn't really seem to have that hook. He's just... a guy without many distinguishing features. Maybe his relationship with his father, but even that seemed to take a backseat to what his father became; the loyalty mission seems like it would have gone off the exact same way even if Jacob wasn't in the party.
That's actually why I disagree 100% with the idea that Jacob is another Kaiden. Kaiden had oodles of character hooks. He got headaches. He had a bad encounter with a turian instructor. He was sexually restrained (he turned down a threesome between femShep and Liara, for chrissakes!) He got flustered easily and was hesitant. There are lots of things you could point to in his characterization. I have trouble doing the same with Jacob... there isn't really anything that stands out, for better or for worse.