I'm not sure any of us can really make accurate predictions about our future based on human history at this point. This might sound a bit nuts, but I see humanity at this very moment as being on the verge of a revolution that will make the industrial revolution look like nothing. I'm talking about information- freely available and readily accessible by anyone, anywhere, at any time. Power in the hands of the people at large, rather than just governments and executives. RAF sort of showcases what I'm talking about- people from different nations and backgrounds are able to come together and discuss things just like this. We've already seen examples of internet information changing the real world in very measurable ways at unprecedented rates, and this is just the tip of the iceberg. I predict that, a century from now, humanity will hardly resemble what we know today. The coming wave of information will roll over everything we have ever known, and no power on Earth- not current education systems, not the RIAA, not the Chinese government- will be able to stand up against that tide for long. I predict thousand-year-old empires simply dissolving in the face of it - it's very scary and very exciting to me.
Human beings have a tendency to gravitate towards perceived power wherever possible, and lately, we're seeing an increasing trend towards both people trying to make their voices heard (see Twitter, for example) and people conforming to peer opinion (see basically anything popular). Basically, I'm saying the future of humanity is equally likely to be run by people who are moral (like most of the people here, it seems) as it is by those who are hateful or just imperialistic.
That said, I don't see it as an easy thing to predict where modern humanity is headed- let alone humanity given help with Andalite faster-than-light technology and morphing abilities. My best guess is that eventually humanity will see relative unity under a centralized "government" with most people belonging to smaller, indistinctly divided "factions" with varying loyalty to each other and humanity at large. All of humanity becomes one big high school with a million cliques
I guess the one word I see aliens species using to describe humans is "opportunistic." If a human sees an advantage to something, they'll take it. It would make us unpredictable and annoying to deal with, but not consistently evil. Depending on who you talk to, you might get people with the ability to look ahead and see that the smartest thing to do is to deal fairly with your species, or you might get the corporate type who sees it as more profitable to blow up your tree to get at your unobtainium (Avatar's probably more accurate than I thought at first). Sadly, humanity's overall shortsightedness would probably lead us to be a race of uncontainable, disorganized conquerors in most cases. The Andalites, Yeerks, Hork-Bajir, any anyone else who we encountered would wind up being exploited in whatever way suits the moment. Sort of a more competitive Skrit Na.