I had the benefit of staying a long weekend at Onsea House while visiting Arusha and it is truly a gem - tucked back off the main road, up a hillside, it has spectacular views across Arusha as well as of Mt Meru. The rooms are extremely up to date and modern (I think they recently renovated) - poured concrete floors, huge bathroom with sunken jacuzzi tub and separate shower, beautiful bedding, etc. I spent time just lounging by their pool as well which is very nice and they do have a full spa with extensive services. But the food and service deserves special mention - everyone is so friendly and eager to make sure you are having the visit you expected, and the dinners are incredible - save room, they are multi course but every bite is delicious and inventive (mostly European and fusion cuisines). I literally held out on lunch one day to make sure I could enjoy the whole dinner. They are also quick to help you with any day trip or town needs. Highly recommend. There were several families in residence while I was there and they all seemed to be having a great time and the staff is good with accommodating children.