Our family of three (my husband, 7-year old daughter, and myself) had such a wonderful stay at this great apartment! We stayed for five days, and this place was the perfect launchpad from which to explore Lisbon, Cascais, and Sintra. You're mere steps from the Castelo de S. Jorge, and just below you (yards away) are any number of shops, restaurants, brunch places, bus and tram stops, etc.
This apartment is a particularly good fit for couples or small families with energetic kids; if you're bringing a stroller I'd suggest instead one of the units downstairs (which are nice, generously sized, and sunny) so that you're not struggling with a stroller up and down.
The apartment had everything we needed, and we particularly appreciated the fridge/oven/stove (which enabled us to make little breakfasts before we headed out each day) and the washer/dryer (which enabled us to keep our packing to a minimum).
Finally, I would be remiss if I didn't mention the view; the photos hardly do it justice. You really are up in the clouds here, with a beautiful vista looking out across the city and the waterfront. If you were to stay in, laze on the couch, and just stare out the window all day, no-one could blame you.