Best bet is to go by your instincts. You will know whether or not you like it.
Also depends what is important to you. Where do the babies sleep? Is there a separate room ? Cots? What is the outdoor space like? What are the staff like? What is the staff turnover? If it is high- why?
Do they supply food, nappies, milk? Do they have a cooked lunch?
When do they change rooms, or are they all in the same room? What prompts the move- age? development?
Just looked at the OP 's date & realised we've moved on...sorry will post anyway in case you're still looking!
Any good nursery will accept visitors on spec, if they insist on you making an appointment then that's a red flag.
We used to ADVISE making a booking, just purely to make sure either the manager or owner (me) were free to spend time with them but we fitted it in around them & the DC's naps. If anyone turned up on spec ( even if we rolled our eyes to ourselves as it was lunch time or nap time!) they were welcomed in but with the proviso it might seem chaotic/ultra quiet.
I'd also ask about staff turnover, (high in some nurseries but there should be a few who stay more than a year!)& what training the staff are given.(motivated staff are better carers)
Also what they do for settling in routines, what's their bad behaviour technique, and how do they communicate with parents. They should have a keyworker system & hopefully you would meet your DS' keyworker before starting.
A good indicator for me would be if the staff talk to your DS as much as you & provide some toys to amuse him whilst you talk. If they just give you a whistle stop tour & bung you some info then I'd not be impressed!
But as tallulah said go by your gut instinct, if you are not happy then don#t go back!!