I haven't used Process Monitor/Process Explorer for a while, are they bringing anything to the table that's not covered by htop? With htop, I can even start tracing a process (using strace) or list the file opened by a process (using lsof) right inside htop. As might be obvious by now, I think htop has a fantastic TUI that also fits its use case very well.

Of course there are other tools that allow deep introspection into what's really going on aside from htop. Another favorite of mine would be perf top, which uses the sampling profiling mechanism to profile the entire system (including the kernel) on a symbol/instruction level. In other words, you don't just see that 30% of CPU time is spent in /usr/bin/cpu_hog, you also see that the time is spent in some_symbol and you can jump right in and see disassemble some_symbol (as long as cpu_hog is not stripped).