I've just spent the past 3 hours playing with the dear girl, swore at her several times, almost threw her in the bin, but climaxed with a moment of great pleasure in Klosters.
Seriously, Heidi is a real bitch, but like all good women is worth the patience it takes to get her into bed, I mean installed. First up you are asked to type a word from a particular line in the handbook. Trouble is it doesn't tell you that when you count line 3 on page whatever, that you must include the title on that page as line 1. It took me several attempts to work out what the word it wanted was (there appear to be 3 different ones and it selects one at random). After 3 attempts you have to run setup again.
Ok, we now have the magic bar on the screen that says 10% installed....20%, 30%, 37% stuck. For some reason from here to 50% setup keeps trying to start in a different window (I had about 5 setup windows open at one point). You need to press cancel over and over to kill the things and allow setup to continue. Next we are invited to tell the software vendor that the CD is corrupted as some of the files are wrong. These appear to be texture files for RHBLaret2 in the various seasons. Clicking "Ignore" allows the installation to proceed. Finally, it comes up with the messages installation complete....... and crashes.
Ok, after a lot of effort she's in bed, so how does she ride? Surprisingly well is the answer. After what I'd read in this thread I was expecting rubbish, but it really isn't that bad.
The scenery might not be quite as good as the Albula (although that route was very short by comparison), but it certainly gives the right feel. There are one or two places that left me feeling "This doesn't look right", where a bit more attention to detail is required, but it's a lot better than some routes that I've seen. I'd say 7/10 - on a par with a good (but not very good) amateur route, but not up to Protrain 1, Albula or S&C 1930 standards. I don't know the line well enough to comment on accuracy (it's been a while since I visited the RhB), but then even Protrain isn't perfect in this resepect.
The trains are pretty good. Externally they are better than the freeware RhB trains (the ones that I used in my Albula activities), but they aren't as good as say Ian Morgan's coaches or Duckweed's steam locos (just my opinion). You might say that this isn't good enough for a commercial package, but I'm sure that many of us have bought model railway trains that are far poorer in terms of accuracy of appearance and accepted them as models. Internally, the two cabviews that I've seen are excellent and certainly add to the atmosphere. The carriages have an interior, but this is nothing special. The sounds are based on the default Dash 9 and Acela, although they have replaced the horns and whistles. The physics feels credible, in that you struggle up the hills, even with a short train. It doesn't feel like you're driving an Acela.
The activities. First point - buy a German dictionary. Even this won't help with some words as they appear to be Swiss-German dialect. Secondly, learn the RhB signals, signs and whistle boards. Once you've jumped these hurdles you're in for a treat. The route has clearly been written by someone who knows about railways and great care has been taken with the signals. The first activity is a tutorial and points out the things that you need to watch out for. In particular, the level-crossings have been set so that if you ignore a whistle board, the activity ends (like on one of the Japenese routes). The second activity is a pickup freight. Just to show that great minds think alike, they too have chosen to start with a train of cement wagons and pickup a lumber wagon.

Just like my Albula pickup activity, it is hard, very hard, due to the steep gradients. I've only tried these two so far, but there are plenty more and lots of scope for some good homemade activities.
Finally, a couple of observations in reply to Ottodad's comments:
1. The point animation is no different to that on the other msts routes (you wouldn't expect it to be) and is perfectly acceptable unless you happen to be a PW engineer.
2. The framerate was no worse than on many other routes. It maintained 14-16 most of the time, climbing to 22 and falling to 10. Now I know that I have a fairly new pc (1.8 GHz with 512 DDR memory), but I don't get any better than this on Tim's ecml (certainly not at Peterborough), not with my settings anyway. Those with slower machines should manage ok if they turn the graphics settings down a bit.
Conclusion - she's a total bitch to get into bed, but once installed she's a gorgeous little model and goes like a train.
Martin