I used NS daily when I was living there, about 4 years ago. I got used to hearing the Dutch complaining when a train was 2 minutes late, or there was standing room only at peak times in 2nd. class, or a train occasionally was a bit scruffy, maybe some litter around the doors, the odd bit of graffiti. My Dutch friends used to tell me that the trains were 'unreliable' and they would rather sit for an hour or so in the appalling traffic twice a day whilst I took a comfortable 30 minute train trip during which I could have my morning coffee and orange juice, catch up with emails, and sit in comfort.
I used to travel 1st. class in and out of work and the compartments were always spotlessly clean and never full. There were usually seats in 2nd too. Compare this with the stinking overcrowded misery of UK trains and there is nothing to complain about.
The only time I recall trains being cancelled was on an exceptionally hot summer day when the rails were stressed so trains had to run more slowly, so they cancelled 1 in 5 in order to assure a regular, if reduced service. This was explained, with apologies, over the PA in Dutch and English.
I sometimes went into Amsterdam and came back in the small hours, felt perfectly safe at the stations and on the trains.
The staff, on the odd occasion when I had to interact with them, were always pleasant and polite and usually laughed off my Afrikaans-oriented attempts at speaking Dutch with a smile and a reply in perfect English.
Since those days I go back to Holland at least 6 times a year and usually use the trains, most recently earlier this week. I have seen no deterioration in service levels.