We are cruise lovers and love Norwegian: we have been on the Sky, Star(3 times), Pearl and now the Spirit (and others will follow!).
The Spirit is an older Ship - but I didn't see any issues with it at all.
Overall experience was very very good.
I found the inside cabin very nice and always clean.
The only issue was the toilet - it did have a mind of it's own on some days - sometimes it just would not flush when you wanted it too - but overall it was a nice cabin.