I don't claim it's the best of the world but calling it expensive and dreadful if just not the reality. Compared to what I have experienced mostly in Europe I found it good and inexpensive.
You should mention the numerous strikes of the RER to give a full picture of the reality then. Because that's a real issue for people who want to rely ONLY on public transports in Paris.
And when it's not a strike, it's the breakdowns. This morning, my commute was one hour longer since there was no train on my line and I had to walk to another one.