At times, yes. It really depends on how much fun the demo is, and how much of the gameplay it reveals. A lot of demos out there don't give me enough time to really see if I like the game, or only give me one small slice of a level. They leave me with a "I'm not sure if I liked that or not, but I want to play more."
I remember buying Shadowrun after playing the demo a ton. Lost Planet, Dead Rising and Left 4 Dead also had memorable demos. I liked them because they let you explore, and they made me want to play them multiple times.
Radeonx said:
Not usually, because demos are only a small part of the game.
And if a company makes a demo, I lose respect for them, because of my unfriendly disposition towards demos.
Really... I usually lose respect for the publisher (since usually it's the publisher that makes the decision to release a demo, I don't think the developer has much of a say in most cases), for not releasing a demo. I hate it when they expect me to pay a full $50-$60 for a game that I didn't even get to try first. When games don't have demos, unless I really know that I want the game and have been looking forward to it, I usually don't buy it or just end up torrenting it or something, because I don't want to take the risk of paying for something that I don't even like.
Although I think demos work better for multiplayer games generally, because if you had fun on the one or two maps they let you play on, you will probably have fun on the other maps, with the others, and with the other gametypes or whatever. But with single player games, one part of it can be fun, but I've noticed that a lot of single player games are fun at first, but then later on the gameplay starts to get to boring because nothing new is really introduced, and it relies on the same ideas throughout the entire game. It's hard to make a single player game that is captivating from beginning to end, and a lot of demos for single player games don't really show if it pulls it off or not.