Please do this trek.
I did this trek from 26 Nov - 1 Dec 2016.
Here's what my itinerary looked like:
26 Nov - Syafrubesi to Lama Hotel
27 Nov - Lama Hotel to Langtang Village
28 Nov - Langtang Village to Kyanjin Gumba
29 Nov - Scale a peak near Kyanjin Gumba, then descend to Thyangsyap Village
30 Nov - Thyangsyap Village to Bamboo
1 Dec - Bamboo to Syafrubesi
This does not include the most painful part of the journey - the 9 hour bus rides from Kathmandu to Syafrubesi and back (practically a full day each). The only alternative (slightly less painful) is via private jeep; there is unfortunately no way to fly there.
The trek passes through forest for the first 1.5 days, following the course of Langtang River - by lunchtime on the 2nd day, the trail opens into a breathtaking mountain valley with light vegetation and shrubbery, affording tantalising peeks of the Langtang Himalayan range over the horizon. The journey culminates in a huge expanse of grassland in a wide valley at Kyanjin Gumba - right in the heart of the Langtang range, with spectacular views of Langshisa Ri to the east, Langtang Lirung and its glaciers to the north, Kangja-La pass to the south, and the rest of the valley to the west.
The region was badly affected during the earthquake in 2015 - much of the damage can still be seen. Langtang Village, once the largest settlement in the eponymous valley, has been partially rebuilt, but remains only a fraction of its original size. For about 20 mins before arriving at the village, you will find yourself walking through the rubble of the landslide which claimed the village during last year's quake.
The trail itself remains open, and entirely accessible to trekkers. Facilities (hotels/lodges/restaurants) remain open, in good condition - and in need of visitors. My guide and the locals tell me that the region has seen a sharp decline in trekker numbers in the aftermath of the 2015 earthquake, which is a shame, considering the beauty of the region. In fact, now might be an excellent time for the trek, with plenty of space available on the trail and in the lodges.
So, the gist of my review is this - please do this trek. It is only slightly challenging, not as physically demanding as some other treks (think Everest BC/Annapurna BC/Circuit), doable within a short window of time (7-10 days), and as captivating as any other trek in Nepal. Most of all, do it to support the locals in their efforts to rebuild the region.