At best case I would give this hotel a low 4*. The finishing touch was very poor, and basically everything was simple colored plastic. It might look cool for a few seconds but then that's about it.
Location is good if you want to avoid city center.

Miles from the centre of Athens. Nice staff. A bit of a plastic palace with a noisy pool area. Rooms are pretty basic but clean and quirky. I have stayed in lots of design hotels and this one didn't really wow me. The worst thing is that locals can pay a fee to use the pool so it gets quite noisy with kids and business men having meetings or talking loudly on their phones.

Very nice hotel
Friendly and attentive staff
Very clean
Free Wifi and underground carpark a plus
Nice breakfast
Spacious rooms and balconies

HOWEVER... whenever I have stayed in this hotel, it is always empty... 30% occupancy at maximum... you need to lower your prices to attract more customers... e.g. lately I am staying at the Y hotel which is around the corner... they have more competitive prices, do offers for frequent customers and even it is smaller the quality is as good.

E.g. Y hotel is 100 euro vs 185 euro in Semiramis

Great concept when build. Now it seems a little worn. we stayed 5 nights in the bungalows, avoid no 521, it is located next to a room with cooling compressors->some noise... Service is great - but matches the price that is high! Very clean. The area (Kifissa old town center) is luxurious and perfect for relaxing.