We went for New Year, which we didn't realise but it's a big thing in Rotterdam - insane fireworks which were very enjoyable (but you probably won't get to sleep until 1am so don't go for a quiet New Year's eve!). There was a huge firework display on the Erasmus Bridge, just round the corner from the flat (like London's) but we were in and settled by 11pm so though we couldn't see the bridge fireworks there were millions of other firework displays going off and the flat has huge windows so we just watched it all from home!
The flat itself is scrupulously clean, very stylish and very well equipped in terms of kitchen (but no toaster so we used oven grill for toast) . I probably could have cooked up a storm with all the equipment Serap has so it was great not to have that horrible thing of 2 pans and one potato peeler when you open the cupboards..... It had a posh integrated coffee maker which we were a bit scared to use but you wouldn't be if you used that sort of thing normally - we just boiled water in a pan for cuppas (no kettle - that isn't a criticism just letting people know). The open plan kitchen/diner was a pleasure to be in. The large windows add to the sense of space and make the flat very light. The netflix and large TV were much appreciated, and the wifi was excellent.
The bed in the double room was very comfortable and the shower was good, the bed in the single room was slightly disappointing - my daughter (16 and reasonably tall) was a bit too large for it and said it was more like a fold up camp bed which moved when she moved and wasn't very comfortable. All in all I'd say that the flat is a joy and a great base to explore from with the Tram and Tube just round the corner - the only slight downer was the single bed so probably best for a smaller child rather than an adult. Serap was a great host and though not there in person answered all our questions speedily and gave us useful local recommendations for food - I'd heartily recommend this flat and this host (and Rotterdam!)