Loved the museum. It's a must visit. Every time I go to Montreal, I always come here, since there is always something new. Just plan accordingly since they may have some random event going on which may impact your visit there...which unfortunately happened to me on my second visit here.
They have all sorts of stuff here, from contemporary, modern, renaissance to the Victorian era artifacts and treasures. My favorite was the Napoleon exhibit. It had really cool old uniforms, pins and medals from Napoleon himself. Plenty of portrait paintings and the Waterloo scene too.
Their contemporary art exhibits are worth visiting too. Lots of Canadian made art can be found here. Pretty cool stuff.