I'm of the opinion that, to a certain extent, anything is better than nothing.
Your lack of walls on all sides may be more of a problem. I have my system in the living room/dining room/kitchen of my apartment - everything run together in one big room with an island separating the kitchen. To top it off, it has a sloped cathedral ceiling. It's next to impossible to balance the speakers to get clean, equal volumes on left and right. The right front speaker is in a corner and the left isn't. I actually notice this more with music than with movies. The rear speakers (which are on stands) have the same problem.
I have set everything up using test tones and an audio meter. But, the settings that work best for that do not sound the best with an actual audio track.
I'm the only one that plays in my living room, so that's not a problem. But I do have to be careful when I leave my LEGO stuff all over the floor.
