If you are planning to invest for a long time then I think it is not so risky. It might be risky for short periods. Along with risk it is also high profitable if invest in strong project based coins.
Well there certainly are some projects that's just die out as the time goes. It's not like a long term will give you additional odd of success in your investment, if the project is a failed project from the beginning other than making you lost your money you will lost the time aswell so it's always wiser to see the project first. However, there's no investment that doesn't involve risk even if it's small risk.