Seestern is a good area for getting onto the autobahns around the Dusseldorf area, has many office parks and there's an easy tram ride into the city. It's not picturesque but practical. I've stayed in the Mercure and the Novotel at Seestern several times in the past as the Innside used to be overpriced. Not now and it's the best option in this area.
The difference was especially made when I had to spend a solid day working at my desk and was very glad to be looking out over a strip of grassland on which rabbits hopped and then 4-storey apartment buildings behind rather than the courtyard of the Accor properties. That residential area is good for walking for a break. The suites have more working space than the rooms (I've now used both) but in both the desk was very good for working at for many hours (unlike so many hotels).
The restaurant downstairs is quite good (unlike the Marriott at D-Hafen, where we've also stayed regularly, which is very unattractively cluttered and where the food is so dismal it takes a storm outside to be wiling to eat there). The barman knew that cucumber was the right match for my preferred brand of gin, which isn't a common brand but which they stocked. Having a car rental desk (Sixt) in the same building is a great bonus: I could pick up a car first thing in the morning, head off and then just return the keys and go up to my room.
Some people might be disconcerted by the layout of the rooms with an internal glass wall to the bathroom area (not the toilet, I hasten to add) but it means that area has lovely natural light and the room feels larger.
Breakfast is pricey, as now seems to be the norm in Germany thanks to tax changes. But there's an Oehem bakery on the main street about five mins walk away which is good for breakfast, light lunch, coffee etc.
The style is contemporary European. (Another disadvantage of the Marriott at the Hafen is its ugly dark, encroaching furniture and while I'm at it, we only used the Nikko once, several years ago, after encountering the filthiest toilet ever on arrival and it taking two calls to Housekeeping to get someone up).
The wellness area downstairs is OK but you wouldn't go there specifically for it.
The suites have a kitchen but there's no equipment in it other than a kettle, so it's of very limited use. The ability to make an infusion was welcome but otherwise there was not even a pot for boiling some noodles or any cutlery. Why not at least a note telling guests that they can get equipment from Housekeeping on request?
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC