The doorbell chimed as Claudia Bruno raised a scalding nip of fresh black coffee to her lips. She set the cup down carefully, hastened from her kitchen to the hall and opened the door. A balding, fiftyish gentleman, half-tail of his partially untucked shirt flapping against his wrinkled khaki pants, barreled past her to the living room, plopped unceremoniously on her flowery indigo sectional and dropped a manila folder on a glass top cocktail table arranged between two matching blue leather loungers.
This is potentially an intriguing start but I concur with the others in that the most intriguing details are bogged down with too many adjectives. I also agree that the man should be named, for the same reasons that Bufty and BrumBall gave.
I may be wrong (please disregard all of this if I'm off the mark) but it reads like you're either describing the scenery in a screenplay, or that you are trying to convey an exact picture in the reader's mind, and that this is what's led to having too much description and detail in the sentences. You don't need to do that. The advantage of a novel over a film is that you can get right inside character's heads and show their inner world.
Also the 2nd sentence is all stage direction (describing what a character is doing blow by blow rather than saying "she went to get the door") - there's nothing wrong with it as a sentence and stage direction can add tension, but too much of it can really slow down the narrative. At the moment what you've got is already too slowed down. It's not a bad sentence though and would be fine if you reduce all the excessive description in the other places. My point is that the stage direction isn't compulsory. Saying "she went to get the door" puts it more in the background so readers can focus on the man who rushes in - who is very intriguing, so you want him to stand out.
Describing the furniture the way you did because this is something Claudia's daughter sees as evidence that Claudia's abandoned the cause doesn't come across that way because at this point, the daughter and the conflict between mother and daughter hasn't been introduced yet. But you can bring characterisation into description by choosing words that your main character might use. If you want to stick with using Claudia's furniture choices as a point of conflict with her daughter, you could use that and introduce the daughter at the same time:
The doorbell chimed when Claudia Bruno had just picked her (brand/type of coffee) from the coffee table her daughter (name) once dubbed "petit bourgeoisie tat appropriated from the workers". She went to get the door. Robert Mencken barrelled past her into her living room, untucked shirt flapping behind him. He plopped unceremoniously on her sofa and dropped a manila folder onto the petit bourgeoisie tat appropriated from the workers.
NOTE: this is not a suggestion for what you should write. I just wanted to show what I mean about bringing characterisation into how you describe what's in the room. It will be much better in your words with your voice and what you know about your characters.
Basically, don't constrain yourself to visual descriptions of every detail. Try to get inside your character's head.
Also the thing of the man rushing into the house like that with a folder is very intriguing. I'd read on to find out more about him and what's in the folder.