1. They both have tortured pasts: Crews was wrongfully put in jail for twelve years, that's right, TWELVE! He lost his wife and his entire life before he was exonerated. Jane, on the other hand had his wife and daughter murdered because of his involvement in the Red John serial killer case (as a fake psychic).
2. They are remarkably calm: Crews has a very zen way of looking at things, he takes his cases lightly but still gets the job done. He talks about things completely inappropriate (like what the last thing a murder victim saw as he was being suffocated - his breath would have fogged up the plastic) but gets away with it because he is just so likable. Jane, on the other hand, is a consultant so doesn't need to follow policy on anything. He has some beer and plays chess with a suspect, and breaks into a house for a case he shouldn't even be working on, he gets away with it because he is always right about these things (though I think he is pretty likable too).
3. They want revenge: Crews spends all his free time trying to figure out who framed him and sent him to jail. He is consumed by this, searching out people who could give him information, bugs peoples cars, and generally gets himself into trouble; he can't life his life until it's done either (he doesn't even have furniture!). Similarly, Jane wants to catch and kill (as we found out not to long ago) Red John, the only person he can't find; he also doesn't have a life and works around the clock solving crime for just the hint of a clue to who Red John is.
Even though the shows' protagonists are so similar, the shows themselves are very different so I am definitely not complaining.