I think it's really just personal preference. I like short giveaways because less people have time to enter, making chances better for those that do. I think it would be fun to pick a popular game and put it up for only an hour. That way, you only have a couple hundred entries where you would usually have thousands (in a giveaway that's 1+weeks long). Then, it's really exciting for those entering. I probably wouldn't make my giveaways longer than just a couple days, but again, totally up to the giveaway creator!

On whether or not this is a good game to giveaway - It's an excellent choice! This developer is making the newest Penny Arcade rpg, so a chance to try their previous games is nice. However, no matter what game you choose to giveaway, there will always ALWAYS be someone on the site that has been dying to play it and will appreciate the chance.