When I think of golf's all time underrated golfers I think of Bobby Locke, Peter Thomson and Billy Casper. Above is an animated .gif of Casper's putting stroke from Geoff Mangum's www.puttingzone.com Web site. This shows that Geoff really knows his putting because Casper was one of the best ever at rolling the rock, but many people forget this.
Casper was an amazing golfer despite being short off the tee and hitting a sizeable hook. But since he had such a great short game and was so consistent with the type of shot he would hit, he was smart enough to take advantage of those assets and become a golfing legend. He was also a European killer when it came to the Ryder Cup.
Casper didn't have the most technically appeasing putting stroke. But I'm guessing he followed the Mangum "formula" of having the clubface pretty square to the target at impact and remaining on the target line about 2 inches after impact. That, and he probably was incredibly consistent and a great green reader with great feel. I'll get a review of Mangum's "Optimal Putting" book someday, but one of the great things he does preach in the book is not becoming overly focused on stroke path and instead becoming more concerned with feel, consistency and being able to read greens (of course, his Optimal Putting book has a plethora of more information than just that).
It's really no different than the full golf swing. It's not to say that all of the other stuff isn't important, but it goes to show that the golfer should really focus on how to improve their impact first and THEN work on the other stuff. Casper's stroke is living proof of that.