Here's what I've encountered so far:
Assyria: I've seen him in about 2/3 of my games. He's a poor warmonger against AI, and usually very lukewarm with me.
Brazil: Almost all of my games. Generally solid builder with semi-weak defensive military, and rarely attacks unless provoked. Almost always on good terms.
Ethiopia: Don't own G&K, so I include Haile. Have yet to come across him in a game. Looking forward to a playing against a religion monger.
Indonesia: Pops up occasionally, but not often. Almost always weak, and a non-player in my games so far. Have yet to see him actually create overseas cities and take advantage of his UA.
Morocco: Friendly, steady player who has appeared in half of my games. Generally loyal and plays wide.
Poland: haven't seen at all, yet.
Portugal: Appeared only once, in my most recent game as Elizabeth. I really enjoyed playing against another naval power-- we were on fairly good terms, and we both made use of ocean trade routes quickly to fill our coffers. Great trading partner!
Shoshone: I've run into him in about a 1/3rd of my games, and I would argue is the strongest civ in this batch. Have yet to go tête-à-tête with him in war, for he's generally friendly. Like his Native American counterpart, Hiawatha, Pocatello can quickly build a large builder empire and hordes wonders.
Zulu: has appeared in most of my games, albeit watered down from his previous Civ incarnations-- I've only seen him go on a crazy murder spree once, and could barely contain his Impi. He's generally friendly toward me, but outside of war, doesn't seem to excel at anything.