ICOs are tools for crowdfunding created by startups.
The token value is somehow pre-set by the ICO, but after listing on the market, it will be only about supply and demand.

If a coin is not desired, it's holders might undersell and the price will drop.
If the campaigns generates a lot of hype, all those who wants a token but missed the ICO might overpay for those coins, as the demand is higher than supply, and the price will go up.