I would endorse all that Joseph, Mads and Philippe have said below, except the wifi does work now, and there is now a shower curtain.
Downsides - it is up 3 flights of stairs, which seem immense after a day's walking around Venice! Once we found out how to adjust the air conditioning, all was well, but make sure you do so from the start.
Upsides - location - 2 minutes to Celestia vaporetto stop, and even though this is a request stop, this was never a problem - just tell the boat crew at the stop before, or press the light on the quay if you want to board. From Celestia there are direct boats to Lido, Murano, Ferrovia, P. Roma and San Marco. Saves a lot of walking. Ospedale and Arsenale stops are about 10 minutes away on foot.
Many parallel lanes to San Marco - 15 minutes walk - and easy access to the Biennale - 10 - 15 minutes.
The area is residential, and quiet, but there are, as others have said, bars and good restaurants nearby.
The apartment certainly sleeps 3 adults, but the second double bedroom has a very low ceiling, and is really better suited to children.
The apartment is well equipped, very clean, and everything works - so no worries there.
Erika was at Celestia to meet us: she is very helpful, and knows Venice well - so you can get some good info on restaurants etc., and her interest in art meant some good tips for the Biennale venues.
Local shops - Punto supermarket 10 minutes away, plus 2 wine merchants for "open" wines - i.e. you fill a recycled bottle - actaully pretty good (and they have empty bottles, so do not panic!)
A lot going for this apartment. We enjoyed our week there.