I do not have (nor have ever had) a S3, but I did go from a S2 to a DISH 622. Its a solid DVR. Its not a Tivo though. I have my other S2 still in my bedroom, and it has the vast majority of my SP and wishlists (as it always had). The HDTV is in the living room, and I pretty much only watch HD shows on it. If it is in SD, I'm watching on my tivo. Granted, I don't have too many SP (or DishPASS as dish calls it) set up on my HDTV, mostly Discovery HD and Nat'l Geo HD shows, hockey and of course Hell's Kitchen. I think I have 13 SP set up on the 622. Overall I would rate the 622 as a poor man's tivo. It does things in a similar manner, does what it needs to, but not much more.
That being said, there are a couple of things that grind on me about the 622. The first is that when you go to record something from the program grid, most of the time it defaults to "all episodes." I then end up with a million recordings of Soundstage, instead of the one episode I wanted. One would think they would set the default when you record from the program grid to just that single episode. The second thing that always bothers me is the fact that if you are watching live tv, go into something you recorded, then drop back to live tv, the recording buffer starts then. When you are watching something you recorded, it does not record to the buffer unless you tell it to record that program. Not a big deal, but sometimes with my tivo, I'll come home, see a program I like starting, tune to the channel, go watch something I've already recorded, then drop back to live tv to watch the show and FF through the commercials. This also bugs me when I drop back to live tv from watching a recorded show and the show that it live looks interesting, so I go to rewind only to remember that I can't. Annoying, but I've gotten used to it. The one other thing that really, pisses me off is that it would seem that the 622 doesn't show live TV by playing it off the hard drive. I believe that it is always recording to the buffer, but if you are in live tv, it is not coming from the buffer, but from the decoded stream. How do I know this (or believe this)? Well, I watch a lot of hockey, am a huge Kings fan, have the center ice package, etc. When the Kings play the Ducks in Anaheim, the Ducks broadcast team gets the game (no Bob Miller!) I can't stand the ducks announcers, so I usually listen on the radio or internet and sync it with the tv broadcast. If the radio/internet broadcast is less than 3/4 seconds behind the tv broadcast, there is no way to sync them. If you get within 4 seconds of live tv, the 622 jumps to live tv. You have to be watching at least 4 seconds behind. Never had this problem with the tivo.
Sorry to ramble on, but its those couple of things that piss me off. That being said, its a solid DVR, although lacking on storage space. Soon dish is supposed to allow you to hook up an external USB drive to save recordings to, but it will cost $40 to enable it. I do like how quickly the guide responds compared to my S2. If you can live with the HD-lite dish has (I notice PQ issues at times), the 622 is a good DVR. Its no tivo, but since I still use my S2 for the majority of SP, it works for me.