For the price, it's very nice. There's a big shower, you've got a little kitchen and the bed is comfy. It's on the ground floor, so no stairs and there's some very nice cafés close by. The metro is about 3 mins away. It's far away from the tourist areas and nightclubs but you've still got a main road right outside your window. Though the sound doesn't get through if it's closed.
I'd recommend this for stays of up to a week unless you're already familiar with Porto.