I've always thought Hill was really under rated. His one problem was he was racing against one of the all time greats. As a bench mark he doesn't measure up well but then he is being compared to possibly the greatest F1 driver ever.
I too, rated Hill very highly and was very dissapointed when he left Williams to goto the back of the grid. At the time, he was the best British driver and was able to mix it with MS.
I felt that Hill took a big step forward in his own developement as a driver, when he was able to keep up with and hassle MS into a mistake in the 1994 Aussie GP. Upto that point, I always felt that MS/Bennetton were a good deal faster than Hill/Williams.