If by "really nice" you mean upscale, then Chez Nous is not that. It is, however, very good and authentic bistro food. I always feel like I've stepped into a Paris cafe when I go in there. It's one of my favorite restaurants in town and the prix fixe is always a good choice.
Aquarelle sounds more like what you're looking for. It's been years since I've been but I thought it was very good.
I also was underwhelmed by Aquarelle. It's not bad, but there are plenty of other restaurants in town where I can spend that kind of money and have a better meal. Chez Nous is really good, but I wouldn't classify it as a "really nice French restaurant".
I have never been underwhelmed with Aquarelle. In fact, I think it is far and away the best restaurant in Austin. That's three hours of pure heaven. I'm sure I'm due an underwhelming experience there at some point, but it sure hasn't happened yet.
p/c le marseillais is a great call. its going to be as good or better than any restaraunt, and affordable too. i just placed order #2203 on their site. i can remember when i was their 3rd order. eric and martine are great folks and they can really cook. i bet i've gained 10 pounds since they sarted delivering to my neighborhood and not just my office, making it too easy to order regularly. nice to see others on here know about them -- they deserve to succeed.