First thing to keep in mind is that many of those "tune up" apps actually cause damage to systems, creating or exacerbating problems in the process. For example, a lot of people right after Windows 8 was released had a number of different problems caused by cCleaner deleting necessary files.
In general, no. Windows 8 is not incredibly buggy. There have been various hiccups, particularly, some people seem to be having problems with certain updates. But Windows 8 has been very solid for the most part.
The vast majority of people that have had problems did an upgrade install, versus a clean install. Upgrades are often problematic and carry over problems that existed in their old Windows, or have new problems caused by an unexpected configuration or driver that wasn't tested.
I have long argued that Microsoft should not support upgrade installs, but they do.. and problems continue to exist because of it.. Luckily, this situation is short lived as most people that do an upgrade do so shortly after a new version of Windows is released.