This script returns the following informations:

• Server name
• OS
• Assigned Memory
• Harddrives
• Total amount of used storage
• Total amount of assigned storage

# Source: http://www.yusufozturk.info/virtual-machine-manager/getting-virtual-machine-guest-information-from-hyper-v-server-2012r2.html
# Usage example: Get-VMGuestInfo -VMName TEST01 -HyperVHost VMHOSTT01
Import-Module FailoverClusters -Force
$HyperVClusterNodes = Get-ClusterNode -Cluster "horhv.bwes.net" | select Name -ExpandProperty Name

$VMs = foreach ($node in $HyperVClusterNodes) {
    Get-VM -ComputerName $node
}
$VMs | select Name, ComputerName | ft -AutoSize

function Get-VMGuestInfo {
    <#
    .SYNOPSIS
 
        Gets virtual machine guest information
 
    .EXAMPLE
 
        Get-VMGuestInfo -VMName Test01
 
    .EXAMPLE
 
        Get-VMGuestInfo -VMName Test01 -HyperVHost Host01
 
    .NOTES
 
        Author: Yusuf Ozturk
        Website: http://www.yusufozturk.info
        Email: ysfozy[at]gmail.com
 
#>
 
    [CmdletBinding(SupportsShouldProcess = $true)]
    param (
 
        [Parameter(
            Mandatory = $true,
            HelpMessage = 'Virtual Machine Name')]
        $VMName,
 
        [Parameter(
            Mandatory = $false,
            HelpMessage = 'Hyper-V Host Name')]
        $HyperVHost = "localhost",
 
        [Parameter(
            Mandatory = $false,
            HelpMessage = 'Debug Mode')]
        [switch]$DebugMode = $false
    )
    # Enable Debug Mode
    if ($DebugMode) {
        $DebugPreference = "Continue"
    }
    else {
        $ErrorActionPreference = "silentlycontinue"
    }
 
    $VMState = (Get-VM -ComputerName $HyperVHost -Name $VMName).State
 
    if ($VMState -eq "Running") {
        filter Import-CimXml {
            $CimXml = [Xml]$_
            $CimObj = New-Object -TypeName System.Object
            foreach ($CimProperty in $CimXml.SelectNodes("/INSTANCE/PROPERTY")) {
                if ($CimProperty.Name -eq "Name" -or $CimProperty.Name -eq "Data") {
                    $CimObj | Add-Member -MemberType NoteProperty -Name $CimProperty.NAME -Value $CimProperty.VALUE
                }
            }
            $CimObj
        }
 
        $VMConf = Get-WmiObject -ComputerName $HyperVHost -Namespace "root\virtualization\v2" -Query "SELECT * FROM Msvm_ComputerSystem WHERE ElementName like '$VMName' AND caption like 'Virtual%' "
        $KVPData = Get-WmiObject -ComputerName $HyperVHost -Namespace "root\virtualization\v2" -Query "Associators of {$VMConf} Where AssocClass=Msvm_SystemDevice ResultClass=Msvm_KvpExchangeComponent"
        $KVPExport = $KVPData.GuestIntrinsicExchangeItems
 
        if ($KVPExport) {
            # Get KVP Data
            $KVPExport = $KVPExport | Import-CimXml
 
            # Get Guest Information
            $VMOSName = ($KVPExport | where { $_.Name -eq "OSName" }).Data
            $VMOSVersion = ($KVPExport | where { $_.Name -eq "OSVersion" }).Data
            $VMHostname = ($KVPExport | where { $_.Name -eq "FullyQualifiedDomainName" }).Data
        }
        else {
            $VMOSName = "Unknown"
            $VMOSVersion = "Unknown"
            $VMHostname = "Unknown"
        }
    }
    else {
        $VMOSName = "Unknown"
        $VMOSVersion = "Unknown"
        $VMHostname = "Unknown"
    }
 
    $Properties = New-Object Psobject
    $Properties | Add-Member Noteproperty VMName $VMName
    $Properties | Add-Member Noteproperty VMHost $HyperVHost
    $Properties | Add-Member Noteproperty VMState $VMState
    $Properties | Add-Member Noteproperty VMOSName $VMOSName
    $Properties | Add-Member Noteproperty VMOSVersion $VMOSVersion
    $Properties | Add-Member Noteproperty VMHostname $VMHostname
    Write-Output $Properties
}





$VMs | % {
    $GuestInfo = Get-VMGuestInfo -VMName $_.Name -HyperVHost $_.ComputerName
    $Harddrives = Get-VHD -Path $_.Harddrives.Path -ComputerName $_.ComputerName 
    $Size = [math]::Round(($Harddrives | Measure-Object Size -Sum).Sum / 1GB, 2)
    $FileSize = [math]::Round(($Harddrives | Measure-Object FileSize -Sum).Sum / 1GB, 2)
    [PSCustomObject]@{
        Name       = $_.Name
        OS         = $GuestInfo.VMOSName
        Memory     = [math]::Round(($_.MemoryAssigned / 1GB), 2)
        Harddrives = $HardDrives.count
        Used       = $FileSize
        Assigned   = $Size
    }

} | Sort-Object Name | ft -AutoSize