It's a McD's that's open (I believe) 24 hours... that should be all the review you need to know what to expect.
There's always a few homeless hanging around the door, as well as a bunch more that will sleep at tables inside during the later hours.
The only time I've gone here was late night, for a mid-drinking pit stop. Which is all McDonald's food is really good for, in my opinion. Laying down a base for the booze.
The staff is about average for a McD's... which is to say, less then agreeable. But in the 90 seconds it takes to spit out, "Medium Big Mac meal, Sprite no ice." Who really cares about customer service? They're probably making less then decent money, working crap hours and dealing with every form of pain-in-the-ass under the sun. They get a pass if they're a bit grumpy.
One night after getting our food and sitting down, me and my friends were joined by a uninvited girl that was clearly tweaking on something. But she wasn't doing anything but telling us stories about how the government abducted here and implanted a tracking chip in her head. To 3 drunks that were there just to shovel greasy burgers down our throats, she was more then welcome entertainment.
But that gives you the idea of the type of atmosphere you'll find in the late night hours in this joint.