Lots of different fighting ability. The small aliens have an effective -1.5, now that they lose all tie rolls, and the normal aliens have an effective +0.5, winning tie combats. That also means that combat with aliens resolves on the first round - one way or the other, somebody dies. Not sure about the statistical effect of the queen's 2d6-pick-one and the predator's optional reroll, but it definitely means that they will feel stronger than the opposition. A queen is stronger than a predator, but not by much.
The question in my mind is how strong that 4+ save for the predator is. You can balance it out by giving the predators fewer models, sure, but the only way to sort the sweet spot for balanace is lots of trial and error playtesting.
Of course, the biggest question is how to organize the turn sequence of a game with this many different factions. Deck of cards? Initiative rolls? Given that each player has a limited number of pieces, the wait time shouldn't be that long, even if you have to wait for five other players. Still and all, probably better to have everybody move, and then everybody shoot, and then everybody fight - rather than one guy doing everything before play passes to his left.
I think that the right turn order will be the order in which the figure types listed. Everybody moves in the order listed, then everybody shoots in reverse order. The predators take their time and then hammer at you - they move last and shoot first. The marines are patient and move only after they've seen what others are doing, but they shoot fast and hard. The minotaurs are tough, but gumpy - they move early, and shoot late. The lizard riders and good, so they can blitz in on most figures, but they won't surprise the marines or predators. This also means that the figures who move earlier in the sequence are effectively slower than other models. The small aliens are going to have a hard time catching a marine that doesn't want to be caught, for example. The marine can always move away from the small alien every turn.
This means that nobody has to wait all that long to do stuff. The humans and lizards have units at either end of the order, and the aliens are clustered near the center. Since everybody does melee at the same time you shouldn't have much down-time.
Does all that make sense?