This is true if you're comparing long-distance trails (certainly there is NO comparison between the AT the the West Highland Way!), but if you want to do some of the major hills in, say, Torridon or Glencoe, you will find them plenty challenging by American standards. Ridges (and exposure) that make the Knife Edge of Katahdin seem like a sidewalk.

I love the Highlands. The scenery is spectacular, and the weather is wildly variable (from hour to hour, as well as day to day). Highlanders claim that early summer (May-June) has generally better conditions than later, but this past year June was quite cold and wet, while August was warm and sunny. Cairngorms are drier (but colder!) than the west, but to my eye, the scenery is not quite as magnificent. Mind you, we are talking degrees of grandeur here.

Absolutely no need to do a package tour. They do speak English, you know (and after a couple of days, you can even understand them ) There are plenty of good books detailing walking routes. Even driving on the left isn't a big problem, since so much of the Highlands is single-track (just what it sounds like, yes).