Anyone cruised on Spirit of Adventure lately?

Am doing the Amazon cruise in march ex Barbados.
Never cruised on such a small ship so any tips?
Also we are preceeding the cruise with a 3 week South American land trip including Machu Picchu so luggage will be bare minimum (we hope) so it would be nice not to have to cart formal wear around.How casual is the ship?
Cheers,John.