Cervaise-
Thanks for detailing out the process by which public art is selected. I hadn’t the stomach for it. You get the Upton Sinclair award for exposing how sausage is made!
To get back to the OP:
As far as the Agora is concerned, from the photos, it passes my test for art on all three counts. I’ll start with technique. Lotsa that. Check. It inspires a feeling- “kinda creepy”, check, and has meaning, check. Is it great? Not in my opinion, but one of the things about art is sometimes time is what does the telling. Lots of artists never made a dime in their life, but their work is priceless both monetarily and culturally now.
I purposely did not read the other reviews yet, but I did look at the pictures you linked. My impression was that the moderately over-sized figures are small enough to be comparable to us, but large enough to overshadow us, to show us that they are really us, just magnified so you can see and take notice. The fact that we are all walking with purpose, but no head or arms? Well, one of the things about art is every person who experiences it experiences it at least somewhat differently, and none of those experiences is always exactly what the artist might have intended. I am not sure that is even possible. In this case, the message is a little heavy handed, IMHO, but that’s ok sometimes. In this case, I feel it weakens the piece. The work seems impactful enough. Not everyone has the budget of a Christo, (And yes, RTA, I am aware that Christo funds his own work) and do we really want half of Grant Park covered with giant headless, armless, people? Didn’t think so. I mean, where would people play ball? There is a reason why Christo’s works are temporary. They tend to take over a place and sometimes they fall on people’s heads.
Now upon reading post Bridget’s fist post, I see I am pretty on the mark, especially considering the artist’s background. I also see that it is a permanent installation. I look forward to visiting it the next time I am in Chicago. The message seems timely. Let’s hope it does not become moreso. 
One thing you must realize about public art is that there are different categories. Some of it merely serves as decoration, and often has no meaning other than beauty and possibly whimsy or drama or grandeur. Some can be very good, but actual artistic merit, well it can rise to it sometimes, but not often.
Other public art is in fact art. The Picasso in Daley Center Plaza comes to mind. The presence of it alone transforms the drab urban canyon into one of the world’s “great places”. It’s image has become iconic of Chicago.
Then there is the dreck, and there is far too much of that, and a lot of that, unlike cans of crap, IS publicly funded.
Rereading my initial post, I was fairly dismissive. My intent was to reassure the OP not to worry too much if the don’t “get it”. Sometimes there really is nothing to get. I was being a little snarky with my point, I didn’t mean for it to turn into a threadjacking dispute about the merits of modern art in general, which has merit, but sometimes borders into sham territory.
I agree with Bridget in that you need to re-experience a lot of art. Pieces can grow on you that you didn’t like at first. If you are from Chicago, you must have spent some time in, or at least passed by Daley Center Plaza. When they first put the Picasso in, a lot of people said WTF? But now, can anyone imagine that space without our beloved Picasso? (yes my location is Burbank, but I still claim Chicago
and, GO BEARS!)
Many cities have guidebooks for public art, and even guided tours, where you can not only get to see some pieces that are selected to be decent, but you will also be given some insight that will help you understand them, and you can discuss your impressions with others as well. Any time you travel to another city, try to squeeze in a half a day to take a tour as well. If you are in the LA area, the entire rail system contains and sometime IS some decent “decorative” public art. Buy a day pass, and station hop. Just stay off the Blue Line after dusk, unless you roll that way
LA also has some decent public art that isn’t part of a subway platform. 
All that being said, sometimes the best way to experience public art is by chance encounter. You are walking down the street and suddenly something totally unexpected is there for you to marvel at!
Happy hunting!