An easily understandable lecturer, who goes into interesting details and the history of your subject. He grades you based on what you've written and its correctness and ideas, *not* to some rigid marking schema. He is very supportive, and his teaching style is unique (at least, in my experience).
I did have him for an Algorithms and Data structures tutorial, and while it was great fun, I found it hard to understand. I should point out that this is not the subject he teaches, and so it may have been my own lack of understanding, rather than anything to do with the tutorial.