I think 2.5* is an excellent description. I have stayed in all sorts of lodgings all over the place - from a youth hostel in Harlem with a shared bathroom with black-stained tub to some swanky hotels in NY & LA. Although of course I enjoy the fancy stays (we stayed at YC in Feb and it was very nice,) we honestly love Pop. We are trying out AoA LM next month and part of me is sad to not be staying at Pop.
We have learned that we want a top or bottom floored room to avoid the noise. We check for bedbugs immediately upon entry in ALL hotels - Pop, YC, NYC 4* hotels, Miami condo rental - because it has way more to do with the volume of visitors than quality of hotels. Our luggage stays in the corridor with a member of the party while someone else checks. We are midday nappers and the overlapping drapes do a reasonable job blocking out the light. A/C is always ok for us, although we wish there was a way for the A/C to activate before we returned to the room. Now THERE is a MyMagic feature I could get behind - "I'm on the bus, activate the a/c!"
Cleanliness has never been an issue for us. I am not a neat freak, but I am a germiphobe, and the carpets are in good enough shape that I have occasionally walked on them without shoes.

I would never EVER do that in a Motel 6 or EconoLodge with their grungy carpets. One of my travel buddies IS a neat freak and I have never heard her complain. We've never arrived to an unclean room. Not to say I doubt those who have had it happen, but we visit Pop 4-6x/yr and I think maybe once we found a wrapper in a drawer. Other than that, always clean.
The size is what you make of it. Four people is do-able. I have travelled with my bestie and: two different groups of close friends, her parents, her brother and sister-in-law, my cousins. All teen-or-above adults. We each pick a corner for our stuff and make it happen. We generally get up in the morning, leave for the park. Come back midday and have already eaten or grab lunch at the food court, then come back to the room (sometimes with lunch, which we eat while trading off in the shower.) Nap for a while, back to the park, back to the room and to bed. We don't go to WDW to hang out in our room, and we are good at just trading off who is in which space. Someone can use the bathroom while someone uses the sink area and a couple of people move about the bedroom. It's not spacious, but it's generally fine.
Spaces: someone's luggage goes between the far bed and the wall, someone's next to the wardrobe, someone's under the window. Can't recall where the fourth goes, I am thinking either shares the space next to the wall or by the table.
It does become more cramped if you need to use an air mattress. Particularly if the person who sleeps on it only brings a double. Oops! (Two adult women, one teen girl and one teen boy = air mattress necessary... not avoiding occupancy limits!)
My only gripe about Pop is Mousekeeping and pillows. They seem *unable* to put the pillows back on the correct bed. I swear they do it intentionally; once I was fed up and wrote a note and they were correct the rest of the trip. But no, Mousekeeping, I don't want my pillow moved to my friends' bed. Yet they put the pillows both on one bed or the other, or just straight-up swap them, EVERY time. It used to infuriate me, now I am just amused... 40+ days of coming back from the parks to pillows on the wrong bed makes you kind of immune. Is that just me?
Is it for everyone? No, if you need "luxary" than it's not going to work. I guess I would prefer to save the cash and come more often. I can afford to come half a dozen times each year on an AP staying at Pop as what it would cost me to come once a year and stay at the Poly. If Pop was "disgusting" then I would make a different choice... but it's not.