Have you seen any of the production pictures or vids?
The ones from blast pit looked superb and that was at least 2 years ago, before the other source engine updates that came in with Portal 2
All you'll see from those is how it looks though - what will make or break it is how it plays.
Besides, I have no doubt it will be good, i'm just saying that I think people are building it up too much and expecting too much - at the end of the day it's not a 'proper' product but I think people are expecting it to be because of what it is. When that happens, unless the thing is bordering on the perfect game, people will just be disappointed because it won't live up to the hype.