The cab stopped at Corporate Plaza, which was located on the surface, above everything. Each major corporation had a building around here, the rich ones even going so far as to construct giant skyscrapers to house their regional headquarters.
John got out of the taxi and looked around sourly. He didn't see the point of living on the surface, not when the sky was a depressing grey, with storm clouds always on the horizon, covering the atmosphere generators. It didn't seem possible, but the air smelled even worse up here, away from the filters. That was one of the reasons he worked for ABCD Corporation. The chance to see green trees and smell clean air was too good to pass up.
The large mantis-shaped Perimeter-Defense security robot at the entrance of the ABCD building watched him with red eyes as he climbed the steps. Its huge head leaned toward him, servomotors whirring loudly.
"John Smith," it grated at him. In greeting?
He grinned up at the behemoth. "Bob, how are you? How's the wife and kids?"
Bob didn't reply. He never did, Jonathan noticed. A giant arm with a pincer on the end activated the door controls. He nodded at the robot and walked through.

There is a...issue of feel for the milieu that comes up. I think that a POV character should usually seem used to the world you create, unless you make him a newcomer. And John Smith (by the way, is that really going to be his name--or are you just using placeholders?) doesn't seem used to the world in which you've set him.

The Perimeter-Defense robot...doesn't come off that well. I mean, seriously think about whether this thing is effectively designed for the purpose you have it filling...and I don't just mean the part where it uses the giant arm with the pincer on the end to activate the door controls, though that kind of sums it all up (hint-a well designed security robot should never need to use any kind of manipulator to work door controls).

On the plus side, your prose is clear enough, and it doesn't have any obtrusively irritating idiosyncrasies. I know that doesn't sound like high praise, but it actually is, in that I would be willing to keep reading rather than writing your story off at this point. While the way you've handled the robot makes me (as a reader, you understand) a bit suspicious of your SF credentials, the teaser about working for ABCD (see above question) being a way to see green trees and smell clean air is effective.