I had encountered this criticism quite frequently with one of my own MC's, whom just happens to be a character I've always loved. I always characterized him as basically a vain and arrogant jerk, but with a sort of comic vulnerability about him, and this is the characteristic that saves him from being totally unlikeable (and lest we forget, one of the most beloved heroines of all time--Scarlett O'Hara--certainly wasn't the most "likeable" person in the world, either). And, as with your character, my MC goes through an arc in which he undergoes much change--and in the end, becomes, if not a better person, at least one more capable of giving and receiving love.
However, I did encounter much of the same criticism. I tended to dismiss it as "knee-jerk" criticism from readers who had not allowed enough time to really get to know the character, and there may be something to be said for this. But the truth, whather we like it or not, is that we only have a few chosen passages in the very beginning to either hook the reader or lose them. In the last few months, I've been working hard on the screenplay version of my novel, and one thing the new medium has forced me to do is to pare much of the material down and to highly concentrate what I do have, including the essence of my character's personalities. What I have found as a result is that much more of what I have called this character's "comic vulnerability" is being allowed to shine through, much more perceptively and much earlier in the story. As a result, even with his pompous qualities still intact, he is much more likeable from the get-go, or--I think(hope) at least intriguing enough to make the reader want to know more about him. And I now feel that I have a much better grasp of how to handle the character when I go back to work on my revision of the book.
So this might be one suggestion. Don't make your character over into something he's not, but perhaps try playing up whatever good qualities he has much earlier in the story, and let us see them. A well-known screenwriter once told me, several years ago, that a key is to have your character perform some act of kindness within the first ten minutes of the story (or, in the case of a novel, probably within the first few pages). He said it could be something as simple and inane as putting out a bowl of milk for a stray cat on the doorstep--in other words, something to show us this person, no matter how crusty, has some qualities we can empathize with.
Don't know if this really addresses the motivation issue, but it's at least something to think about if too many people are calling your MC unsympathetic. Another example I can think of is the MC Jack Nicholson played in "About Schmidt." The character was basically a curmudgeon and the epitome of an aimless man with no direction in life and nothing really good to say about anything or anyone, yet the story is propelled into motion when he begins sending checks to a "starving child" in Africa, which of course becomes his real redemption in the end. I think readers will be much more willing to give the benefit of the doubt if--as someone else on this board previously pointed out--you give enough hints and indications early on that this character has hope. Readers like to have some indication of such hope before they invest heavily in a character; to feel that there is going to be some "pay off" in the end that will make sticking with them worthwhile.
but unmotivated is something else entirely, and I wouldn't be comfortable with that.
