Frankly, Jacob was one of the only new squadmates that I felt like I trusted on my first playthrough.
He's calm, cool, collected, and even though he works for Cerberus, you can tell that he isn't like Miranda at all. He's doesn't have the air of superiority hovering around him. He's just practical, honest, and most importantly, capable.
Sure he has daddy issues, but he even manages to resolve that in a healthy, responsible fashion.
No, he isn't "the most interesting" character in the game, but he strikes me as one of the best representations of a normal human in a world otherwise filled with extremes. That makes him easy for me to identify with.