Oh, that's a great question. Honestly, the most frequent complaint I hear—and honestly, I've made it myself—is about overflowing bins. You walk up to a public trash can on a busy street, and it's just packed. Stuff is spilling out onto the sidewalk. It defeats the whole purpose and actually creates more litter. It just looks messy and can smell pretty bad, especially in the summer.
A close second is the smell. When bins aren't emptied regularly, especially around food areas, the odor can be really unpleasant and even attract pests. People also often mention that there aren't enough separate bins for recycling. They want to do the right thing, but if there's only one general waste bin, everything gets mixed together.
Finally, location is a big one. Sometimes the cans are placed in odd spots where you don't really need them, and then they're missing in areas with high foot traffic, like near bus stops or parks. It feels like the city isn't quite matching the service to the need. So, in short: overflow, odor, lack of recycling options, and poor placement. Getting those things right would make a huge difference in how people feel about their city's cleanliness.