I've only been there once, Eindhoven and Rotterdam. I really liked it, especially Eindhoven, it was so lovely to spend time in, friendly, welcoming, chilled - and there were almost no tourists too. The train journey between the two cities was interesting and pretty, Holland really is as flat as they say it is.
I wish I'd tried the local cuisine though. I couldn't really work out what most things were, so I just ate the English dishes.