I recently completed the Manaslu Circuit trek with World Expeditions, and it was a wonderful experience in a beautiful but fragile place. We were a group of 8 trekkers supported by a terrific team of 14, including guides, (excellent) cooks, kitchen-hands and porters, expertly led by Rishikesh Nepal. The cooks prepared tasty and varied food, in sometimes tough conditions, and no one in the group got sick, beyond the occasional cough.
The Manaslu trek offers a great range of landscapes to experience. It starts low, at an altitude of about 700m, with warm days surrounded by fields of rice and bananas. After a few days passing through small villages in deep valleys, the landscape became more Tibetan, with fields of barley, yaks, chortens and mani stones; the conditions are colder and the big mountains are much closer. The day crossing the pass at Larke La was a highlight - a long and tiring day but we got to experience the pass in incredible still and clear conditions, all to ourselves.
The walk out is shorter and steeper - mostly down, thankfully - through beautiful forests.
The Manaslu Circuit trek is not as busy as the well-known Annapurna treks nearby, which meant we usually only needed to share the trail with locals, mule trains and the occasional small group of other trekkers.
A great trek to experience, and highly recommended.