As someone who occasionally has to write PowerShell, I can say with confidence that is an abomination of a language with a horrible syntax. I hope this never gets implemented on any other platform when there are so many superior alternatives.
ps OUTLOOK.EXE | kill
I'm a Unix guy. Window Server 2008R2 still requires reboots for trivial activity (eg, installing Office web), which I don't think is appropriate for servers. But PoSH is awesome.
The bottom line is this: If you need a tool for operating on objects, then use a programming language; preferably choose one with a strong REPL. If you need to deal with persistent, serialized, streams of bytes, use a traditional shell.
It's far too verbose. It's a shell, and a huge pain to type interactively. Yes, it has tab completion, but so does bash - and that's far less verbose.
It's also opaque. Because it's object-based, but you work with it on the command line, it outputs in text but there is constantly "other" information that is not displayed on screen that you can get if you pipe through to another command. That's not intuitive. Text processing is intuitive.
It reeks of design by committee. It's own execution policy. Java-like getter/setters. Super verbose syntax. About the only good thing PowerShell has done is force Microsoft to provide a command-line, scriptable interface to all their server products to get away from GUI dependency. And that's a product of their PowerShell internal policy, not the language itself.
Yes, it's better than CMD.exe. But still a huge pain. Other platforms have Python, Ruby, Perl... and dare I say it, bash.
Now that there may be a prospect of using PowerShell on other platforms, I wonder why I'd bother? Day to day tasks I'm perfectly happy doing in bash, and anything more complex, I'd just as soon use Python, Ruby, PHP or Perl.
diff is an alias for Compare-Object so if you tried it, you should have seen it do something. But unlike actual diff it operates on objects rather than files, so you need to gc (Get-Content) the files you want to compare.
sed/awk: string manipulation is built-in to PowerShell, but sed's in-place file editing is replicated by piping Get-Content into Set-Content. Sometimes more verbose, sometimes not.
I personally don't see what value PowerShell would bring to other platforms, given they already have huge swathes of scripts written in well-developed (or at least well-discussed) languages and command-line tools for system administration are plentiful. But why would you bother using Perl when you already have Ruby? Obviously some people will take the choice if they know it.