The Maasvlakte is usually a waste of time, and I don't think the industrial landscape is too attractive.
Depending on how far you want to go, but these are some very nearby areas I'd recommend:
To the west: Voorne-Putten, Breede Water & Quackjeswater - some of the best dunes in the country, breeding Black-necked Grebes, Spoonbills & Little Egret, plenty of Nightingales, quite probably Bluethroats etc.
To the east: Kinderdijk - Black Tern, Purple Heron, chance of Savi's Warbler, and more windmills than anywhere else in the country. Quintessentially Dutch.
To the south: Goeree-Overflakkee and Schouwen-Duiveland have plenty of places to go to (all within an hours drive from Rotterdam), with Kentish Plover and plenty of waders.
Just a bit further afield, near Breda, there are forests where Black Woodpecker should be easy.
To the north: Starrevaart (near Leidschendam) can be rewarding; Reeuwijkse Plassen has a few Great Reed-Warblers.