Imperialistic is fine, I think. Great Generals are pretty darn good, and I don't think I'd ever be disappointed by getting more of them (settle a couple in your heroic epic and iron works cities and just tell me that isn't game-altering). They're good for adding as great instructors, and great for leading armies (having one unit that's either a super-medic or guaranteed to win is quite useful in war).
The settler bonus isn't quite so important, but supposing you maximize production around your first couple cities, it works out quite well. With just food, it's obviously not quite so good (although I bet they patch it to give the bonus to food production).
Considering that a good half of my armed forces (usually the attacking element of my army as well), comes from my Heroic Epic+West Point city, settling a great instructor in there effectively gives all your units that matter (aka will be attacking rather than garrisoning or providing support) +2XP for each great instructor. Effectively, this trait either augments more agressive traits (like agressive or charismatic), or allows a builder-ish civ (like the romans, for example) to host a compotent and capable military. Sure, other people get GGs too, but you'll be getting about 50% more, which can really add up. Overall, I am not disappointed. I don't think it's an absolute power trait, but it's darn handy.