In my worldwide Starwood stays, I've never been as let down by both the guest experience and snippy post-stay follow-up with the Hotel's manager as I have at the Westin Paris.
It's a real shame as it's a great location with so much potential.
CDG Sheraton may not have the ambiance as the other Paris properties, but the service & Elite recognition is top notch.
Remember, Starwood has a lot of competition in Paris from other chains, trendy boutique hotels and quality B&B's so it pays to shop around.
(this post was originally in a thread called Paris Master, NOT Westin Paris Specific)