Open task manager and
... oh that's right it doesn't support per logical cpu like 7 does so you can't tell if a single threaded app monopolies a core. Resource monitor for that.
Have you actually used the Task Manager on Windows 8? The improvements in the Windows 8 task manager is one of the major improvements over Windows 7 in my opinion.
The default "out of the box" view on the Performance tab shows a single graph summarizing processor load, but clicking on the graph provides several options to customize the graph including an option to display a separate graph per logical CPU core.
This appears to provide just as much information as was available in Windows 7 but in an easier to read format - especially on systems with 8 cores or more.
There is also an option to overlay the amount of time spent in the kernel and in multi-socket systems there is an option to group the graphs by NUMA socket.