Well, this depends. Personally, I have extremely rarely experienced any severe system problems, because I allow my Mint systems to install all updates as Ubuntu would do. I.e. All 5 security levels are marked "visible" and "safe" for installation here.
In Janaury 2013 a bug affected kernels 3.2.0-36 and 3.5.0-22. It was fixed two kernel updates later. This was the only regression which affected my systems like any system using the 2 kernels. - Yet, other users may have had different experiences. There is no warranty.
On the one hand, level 4 and 5 updates are supposed to fix bugs which affect really low level software, kernel and hardware drivers. On the other hand it is possible that what fixes a problem for one user will create a different problem for another user.
To be honest:
I hardly ever allow kernel updates to be performed the same day the new kernel has been released. I tend to wait for about a week monitoring the Mint and the Ubuntu forums for bug reports related to the current kernel update.
Endless legions of bigoted, brutal, bloodthirsty Orcs from the dark land of Mordor are bringing desolation, despair and death to the poor inhabitants of the Middle East.