Preface: I am a 'hard marker' and very critical where I think the tour operator could be better. Having said, I have absolutely ***NO*** substantive criticisms to make after our 2 week tour, starting in Hanoi.
Our guide met us at Hanoi airport late at night (having met other straggling incomers during the day) and this set a precedent for individual and collective caring under his shepherding for the next 2 weeks -- nothing short of superlative. From Florence Nightingale to facilitator to problem-solver to advice on restaurants to guiding itself, Thien's leadership was beyond-ordinary. We all felt very well looked-after and safe.
If I have a criticism, it could be the micro-management of one's time so as to get everyone organized for each side-trip. However, if we weren't time-managed, we would never have seen and experienced as much of the sites and the local culture as we did in the time available. Take one's pick!
As a previous commentator said (and I agree with just about 100% of what he said, (and I'm trying not to repeat it), there were some 'dodgy' landings in remote locations, but staff did their best. If you have disabilities, double-check before you leave.
The side-trips they chose for us sounded very ho-hum in some instances (snack factory, brick plant???) but none of them was to be decried after the event. They have carefully chosen those that exemplify the local customs and everyday working lives of the locals to very good effect. If you go, don't opt out! You may be nicely surprised!
There are many, many bright young children who (especially in Cambodia) are short of good teaching (largely because of the extermination of the professional, middle-classes by Pol Pot). Whereas I became a little "orphanaged-out" and not a little pressured as to the generosity I could willingly bestow to thoro'ly deserving causes, even I (as a hard-nosed bastard with Scottish blood) found my heart and soul touched. so much so that I plan to return a year hence to teach, as a volunteer, English & whatever else they can draw from me as a reasonably widely educated person in my 70s. If you don't want your heart and soul touched, don't go on these side-trips, but I challenge you!
As to the "main-course" visits, such as Angkor Wat itself, museums, obligatory national monuments, etc., hang in there! The guides were very accomplished in informing you of the histories concerning each, and -- if you are willing to learn -- each paints a pixel in the big picture of what has forged these countries.
Expect to come back exhausted, yet fulfilled, better educated and appreciative of these historic cultures and their evolution to the present day.
Thank you Viking, and especially to our Thien.