Ondaatje is a poet. He's good at giving us a sense of this war as a tiny incident in a history of thousands of years- but not so hot on politics and class and all that stuff that is the novelist's bread and butter. Yes, the government is as guilty as the rebels- but who are any of these people? What do they believe in? What are they killing for? In a perspective of millennia these things may not matter very much, but here and now they do. It's fine for the characters to be ignorant of the thing they're caught up in, maybe not so fine for their creator.
Some humour would have been nice. Humour is how human beings have traditionally coped with horror. The ending- beautiful though it is it is- is a steal from Tarkovsky's Andrei Rublev.