They are not as bad they were in Windows 8 (where I think I never used a modern app for more than 10 minutes) and much better than what I had in Windows 8.1. The Mail and Calendar applications are great. As are the Office Mobile apps (free for devices under 10.1 inches and only accessible if you have an Office 365 subscription on devices with screens bigger than that).
It’s a great thing that the modern apps don’t launch in full screen by default. Unlike before when you’d have wanted to stay away from any product of the Windows Store, in Windows 10, there’s every reason for you to want to give them a try. Word of advice: start with Fresh Paint.