Well, I'm not sure if I have had enough time to give a complete opinion, especially riding in deep powder, but I can say some things.
1) The difference in power between my '12 and this sled is amazing! Not sure all they did in that time frame, but the power and responsiveness in 800 in the Riot is incredible. Hard to believe it is an 800.
2) The mono rail does make a big difference, as one might think. It is much easier to roll it over in both powder and just soft snow. So the amount of energy required of me is less, which is a big thing for me and my poor heart!
3) The track is great! They always have been.
4) The sled is a pretty good crossover. Probably more of an off trail with the 2.6" track, but scratchers are standard and down most of the time I am not in powder and I have not had any issues with the engine getting hot, even riding trail 13 between Twin Lakes and Greenland when it was super cold and the trail very solidly packed. It does roll over more easily on the trail too, so not a good sled to be expecting to be a Ricky Racer-Trail Tamer with, but fast trail riding has not been for me, at least with any kind of turns involved.
So I guess, as a whole, I am very happy with the sled. It is about perfect for what I want to do, which is mild off trail (no gnarly stuff in the trees on hills) and trail riding to get there. I am quite surprised that when the mono rail came out, it was not a bigger deal in the industry, but it seems like there is a bit of herd mentality in snowmobiling. Right now that mentality is Poo and Doo hit homeruns with just about everything they do and AC/Yamaha are just there for someone that wants to keep riding those brands. I am not brand loyal at all and do think that Poo and Doo make great sleds, but some of the things that get hyped in the rags with regard to those sleds seems to be over-hyped in my opinion and I think the mono-rail was a bigger deal that it got credit for.
-John