I liked the demo, but I wasn't as wowed by it as I had expected to be.
The final game however, is easily my game of the year.
I felt kind of the same way towards Twin Snakes as I did the demo. I consider it a good purchase and I'm glad I have it, but it doesn't stand up next to the original and MGS2. MGS3 on the other hand, I believe to be the best in the series.