I made the switch last week and had D* installed on Friday - pretty much identical config to the OP. After all the horror stories I had heard about installers showing up with wrong gear, setting things up incorrectly, etc. I was a little concerned. As it turns out, the installer showed up EARLY, with all the correct equipment. He did everything just as I asked (and probably a thing or two he wasn't supposed to do) and left everything neat and clean - very personable and professional. However, for some reason he thought the only reason the system needed an Internet connection was for the on demand stuff and he wasn't going to put it in when I told him I really didn't care about the on demand stuff at this time. When I explained there were other things the connection to my home network was used for, he went ahead and installed it.
I, too, noticed a much better PQ in HD, but the SD leaves a bit to be desired (fortunately I don't watch much SD). The HR24 receivers come with the RF remotes which was nice so the receivers can be hidden out of the way. The UI is a bit different than I was used to on the 722, but I don't think it is any worse. My only real complaint is with the guide - even when viewing "Only channels I get", it doesn't filter out the "pay" channels. I know that I can create a custom guide, but that is a real pain - especially having to do it for each TV - and there are only two custom guides available.
The MRV is great, but I'm still struggling with programming and getting things distributed among the two DVRs so there are not conflicts - this should be something that could be improved upon in a future software release. I really like they way they do the networking. I am a little disappointed with the mobile phone apps in that communication is 1-way and not guaranteed. DirecTV2pc won't work on my 2.5 year old laptop and apparently doesn't really like wireless networks either - I have not tried it on my wife or kids laptops yet, but it will be a really good feature.
It took me nearly 3 years debating on switching from C* to E*, but once I did my only regret was not doing it sooner. I have been debating switching from E* to D* for about a year now - once again, I am wondering why I didn't do it sooner!
One more thing... to E*'s credit, the cancellation process was smooth (so far). I was able to cancel via a chat session and didn't have to call in. I have a transcript of the entire dialog. There was no cancellation fee, other than $15/receiver for return shipping *IF* I use the enclosed call tag, but I can ship them back using whatever method I choose, though I am still responsible for shipping and insurance.