I think Valley is pretty good. The environment itself is the most good looking out of all the environments in my opinion. Also, the birds and wind turbines add some life into your track, since everything isn't completely static.
I also like the various blocks you can use. There are a lot of possibilities you can do and there aren't many blocks that feel "useless". It looks like there will be many more blocks to come into Vally too (well I think anyways, because there are only 6 root categories to choose from so far.
The music is good too! My favorite is the one in the day time that sounds kind of 80s style.
The Valley car's handling is pretty tough, well, on sharp corners and dirt roads anyways. I was hoping it would be more arcade like. Oh well, I think it will get better with practice though. For instance, the first time I drove on dirt in the Valley environment, I thought "this sucks", but after some practice, I am beginning to understand how to do the dirt driving and enjoy it. I find that the Valley car is easier to control on roads than the Canyon car, maybe because the roads aren't as bumpy and the car doesn't have a ground magnet on the roof of it?
Neither Canyon, Valley, or Stadium crashed on me so far (crossing fingers), even on my laptop. Maybe because I don't use custom images, music, etc. I don't know, I'm not too sure why it would be crashing for you guys, but I bet Nadeo will come up with a fix, just inform them what's happening.
Also, I think the price is very reasonable for these games, especially Stadium. People pay $1 for a hat in uncharted 3, or $100 for a rare hat in Team Fortress 2, so why is paying $10 for Stadium unreasonable?