Kal ho naa ho is a great story combining laughter and tears to perfection. Some viewer comments strangely focus on SRK's far-from-realistic performance, totally missing the point of this film in my opinion.
It goes way beyond technicalities such as realism, along the lines of a fairy tale dealing with a multi-dimensional range of emotions and relational situations at a deep symbolic level, somewhat reminiscent of the french new wave of the 60's at its best.
Poetry should not be scrutinized for its lack of realism but rather taken in from a distance, its inner message interpreted at a more intellectual level, with candor and an open heart. A such, kal ho naa ho hits the mark much like a wonderful display of fireworks.