The effect on the skyline is obvious from most places in Paris, as you can see in this picture from the Jardin de Luxembourg.
You can see from the surrounding streets how badly the tower fits into the traditional skyline of Paris. Expect similar visual blight from other high-rise projects being planned within the Peripherique.
The effect on surrounding streets is not as well known. The complex with the Tour Montparnasse also includes the Gare Montparnasse and a shopping center named the Galeries Lafayette. Here is a view of the complex from a nearby street.
And here is a view of the nearby traditional streets from next to the complex.
The effect on the skyline and the effect on surrounding streets are both typical of 1960s modernism, which ignores its context completely.
Today's avant-gardist architects often defend one hideous project or another by saying, "People also disliked the Eiffel Tower when it was first built, and now everyone loves it."
There is an obvious answer: "People also disliked the Tour Montparnasse when it was first built, and everyone still hates it now, fifty years later. Your project looks much more like Tour Montparnasse than like the Eiffel Tower."