NO. but its probably couse I don't play just any games.

Yes. XBLA games live and die by the demo for me. Braid, Castle Crashers and Lucidity all became buys the second I tried the demo. Like wise, the Turtles in Time remake kept me from buying it.

The Brutal Legend demo didn't do much for the first time I played it, but I played it again a few days later, and enjoyed it a lot more. It actually went from a buy when I first heard about it, to a no buy when I played the demo the first time, and back to a buy again when I played it the second time. I think I just need to be in the right mindset when I play that game.

I pressed no. And I MEANT TO PRESS YES!! lol
Anyway

It always decides whether i buy the game or not. I couldn't really tell you about one exact one, coz i've played like 1,000,000,000,000 demos in my time....but...urm....battleground..i think was the best one.
I was like...great..another shitty war game thats ripping of MOH and COD...but it was so good. And i played it for AGES!!!
Really old one though, but it wasnt a rip off, just different..

A more recent one...Star Wars a clone wars for xbox. I was expected it to be really good and inventive...and then i downloaded the demo on my xbox.....i cried. It was hilariously crap. Given the force push was impressive, but you could hardly personalise your movements....Yeah

RANTING DONE!!!

No. Sons of Liberty. The game smple was the first portion of the game where you play as snake. When you trade off as raiden later in the game the controls are the same but gameplay itself killed the game regardless of main character change.
Because of this I don't let game samples lead a full reveiw untill it's out.

Well right now I'm playing the uncharted 2 Demo and let me tell i have been hooked to this game for 5 days now. I'm just waiting for the game to come out and see how it goes

there have been many a' games that the demo was either a really shitty interpretation or an awesome first hand experience for any up coming game.

there's been PLENTY of times that I get the demo and i'm like "ok this is good, fuck! wow! this is real good!" then I buy the game and it's like "ok... where's the awesomeness that was in the demo?"

Sadly tho in my case, there have been more let downs after the demo experience than the good ones... 1 good one: Uncharted (shit is BANANAS!!! I can't wait for Uncharted 2) // bad experiences seem to be in a lot of racing games or in most games that repetition seems to be what the game's all about...

Don't get me wrong, I LOVE RACING GAMES! but wow... WOW! Gran Turismo better be the best fucking racing game I ever play...

The demo for ICO was good. Had me hooked so I was sure the game was going to be awesome...let's put it like this. There were parts that were awesome and parts were you reminded yourself (repeatedly) that you needed Yorda.