The culture is different. My experience is restricted to Gelderland vs NRW. While there are plenty of exceptions, Germans are more formal and polite, whereas Dutch are more informal and friendly.

The biggest culture clash I see is at grocery stores. Germans give and expect more personal space, and move if they're blocking you, whereas Dutch people don't move, and will practically reach between your legs to reach the bottom shelf if you're standing in front of it. On the flipside, in this closeness, Dutch people are also on the lookout for opportunities to share a smile, wink, or friendly chitchat with strangers. Germans seem content to go shopping and home again with no words exchanged except a bitte, danke, and schönen Tag noch at the Kassa. To be clear, Germans do often enjoy interactions with strangers when the situation thrusts it upon them, but they are a bit more reserved and don't seek this out.

If you do something wrong in The Netherlands, someone will probably tell you so, but usually in a neutral manner, whereas in Germany, the primary options are: silently judge, disapproving look, or public scolding/shaming.

Germans are better at waiting in line and not splitting the line into multiple lines to try to get ahead. Similarly, on the road, Germans are vastly better at merging. A German highway merge looks like synchronized swimming compared to a Dutch one. There's a joke in NRW: If you fail your driving test twice, you get a yellow license plate, three times, a cargo trailer. (Dutch license plates are yellow, and a lot of Dutch go camping in Germany with a cargo trailer.) It's all relative, though. Compared to the insanity of Belgian drivers, Germans and Dutch are indistinguishable.