Client-side SharePoint PowerShell - Get list items - The collection has not been initialized

On SharePoint 2013, I am trying to get list items, with client-side SharePoint PowerShell. Even for field Id or Title, I encounter this error: The collection has not been initialized. I don't know how to include fields. I find many exemples in C# or JavaScript but none in client side powershell.

Here is my code (it returns correctly the number of items):

Function New-Context([String]$WebUrl) {
    $context = New-Object Microsoft.SharePoint.Client.ClientContext($WebUrl)
    $context.Credentials = [System.Net.CredentialCache]::DefaultNetworkCredentials
    $context
}

Function Get-List([Microsoft.SharePoint.Client.ClientContext]$Context, [String]$ListTitle) {
    $list = $context.Web.Lists.GetByTitle($ListTitle)
    $context.Load($list)
    $context.ExecuteQuery()
    $list
}

$context = New-Context -WebUrl "http://mysharepoint.com/sites/qp"
$list = Get-List -Context $context -ListTitle "QP-Configuration"

$query = [Microsoft.SharePoint.Client.CamlQuery]::CreateAllItemsQuery()
$items = $list.GetItems($query)
$context.Load($items)
$context.ExecuteQuery()

$items.Count
$items[0]

foreach($item in $items)
{
   $item.Id
}

$context.Dispose()