From time to time we get sent discs with preview code from various developers or publishers that features an upcoming release, and regrettably the experience of playing it is not always as exciting as it's made out to be.
Typically, it's in a distressed state of construction with various pieces missing. It's almost always prone to crashing, there are entire segments that are out of place and it's a safe bet to assume nothing is entirely the way you'll see it in the final game. Along with any form of refinement, an explanation as to which particular aspects require more work is almost always missing as well, which gives you a sort of "game within a game" experience as you mentally dissect every glitch and try to determine if it's something that will get fixed, or something that will be released as an "exciting new feature". And then you have to comment publicly on which is which.