Jen -
I have always thought that if you are someone who really loves Disney's attention to detail, you will love ToonTown. ToonTown is a treasure trove of those famous Disney details, hidden gems, inside jokes, etc. A lot of people do not like ToonTown at all or they disregard it as just being something that is for kids only. Sure, it is mainly aimed at kids, but I think there is a lot to see. The main problem I have with it is that is usually soooo crowded, and it doesn't stay open as late as the rest of the park. So you may not be able to actually see too much in ToonTown if there are tons of people in your way.
ToonTown is the sort of place where you have to look at everything and pay close attention, because there are sight gags and jokes in everything. Everything is a play on words or a whimsical, amusing surprise.
Yes, there are manhole covers that talk or make noise when you step on them. Also, make sure that you push any button you see, pull any lever you see, open any box that has a lid, turn any doorknob handle, read every sign, etc. There are jokes everywhere. It's a very interactive land. Even the designs of the facades are playful in that you might look at something and think it is just a door at first, but when you step back a few feet from it you realize that the door was designed in such a way that it looks like a face. Things that just look like wacky ToonTown designs often times are really faces that you catch when you look at them from a certain angle.
Christmas time in ToonTown is especially fun because all the garlands and wreaths around the land have little items hanging from them that are relevant to their specific area. Like, for example, at the firehouse you will see Dalmatian-spotted ornaments in the garland. Above the "dentist office" you may see a wreath with teeth in it. Pluto's has bones in the garland. Daisy's has daisies, the bank has garland with money it, etc., etc. Everything is very cleverly done.