Do you approve of Nicholson's actions?
I may be in the minority here, but I think the film actually showed Nicholson's actions in a good light. His strict view that his officer's not be forced to work may seem silly nowadays in a post-Aristocracy world, but in those days it was not so far fetched.
It seems the British mentality that once you give up your laws you begin to give up your very self and morality. Nicholson's firm stance on the matter led to a boost in the morale of his men, and stopped the Japanese guards from conquering the men's self esteem.
Nicholson's obsession with building the bridge, while a side-effect of his time in the Oven, was not particularly a bad thing. Like he stated, it gave his men something to do to keep their morale high. Every one needs something to work for, and in a POW camp there is little else that you can.
It is of course regrettable that Nicholson's obsession with the Bridge meant that he could not work out what was going on in the end with the explosives and didn't realise it was a British Operation, but Nicholson still did the right thing in the end, once he realised what was going on.
The deaths of Shears and Joyce (and his own) were regrettable but accidental. There was nothing accidental about the upkeep of morale that Nicholson created in the camp.
I consider Nicholson a hero and nothing less. His mind perhaps wasn't there, but his heart was in the rightest of places.
"Are you sure it was a book? Are you sure it wasn't nothing?"
"Oh yeah."