Always interesting to read others' comments; remarkable how perceptions differ.
What should NOT be surprising - Boston is a popular destination for both American & international travelers. It's also home to many immigrants, the vast majority of whom are legal. You WILL encounter them everywhere you go, and some may converse loudly. Such behavior may detract from your experience anywhere and are no reason to rate the attraction poorly. (BTW, if you have acquaintances from other countries, ask them what the typical American sounds like to them.)
Maps are readily available for the asking at the "base" stop and on the trolleys. Yes, it's a one-way, circular route. No, Boston doesn't allow them to post signs, but 1-they always pick up where they drop off, 2-the other companies pretty much follow the same route, and 3-they come along every 10-20 minutes so if you don't see'em, you're in the wrong place!
They also are available on the website for access from a smartphone. My advice: Look at the map BEFORE you ride, to decide which stops you're interested in--DON'T expect the driver to be your only source of information.
Perhaps one of the most interesting aspects of "hop-on-and-off" tours is that you will likely encounter more than one driver/guide. The company provides a basic script but different guides have different styles. Some, unfortunately, may be off-color. The guides are in part working for tips, and I would think that over time the offensive drivers would learn that their scant tips reflect riders' disdain. Alas, my worst driver stated he had worked for the firm for over 10 years.
Overall, this was a great way to get an overview of the geography and rich history of one of America's oldest and most diverse cities! My family went from "ho-hum" to "when can we...?!" in the relatively short time it took.
Two final comments: look for coupons and Groupons, and watch out for late-in-the-day runs, as each trolley only holds 40 and everyone is trying to get back to where they started--you may have to wait awhile.