The two-player game went well; the four-player game bogged down and we aborted it. The next logical thing to try was a three-player game, which Alaric helped us out with this weekend.
We had in play the purple reptiles and the other two sets that were not "dogface". (One of these days I'll learn all the names.) One of the other players was the best (potential) herbivore and the other was the best (potential) carnivore, leaving me in the middle. Each species has advantages and disadvantages; I just haven't learned them all yet.
I went into the water, which seemed like a good idea at first but then the others started crowding me out. After one turn in which I was down to two counters and no obvious growth path, I was ready to resign but agreed to keep playing. In the next turn (turn 8, I think) we got a disaster that ended the game. Oops.
That took about an hour and a half, so we decided to start again. I suggested we juggle creatures around; in the end Dani and Alaric kept what they had and I swapped the lizards for "dogface", a mammal. Dogface's special trait is that individual creatures, as opposed to whole species, can be declared herbivore or carnivore. This seems nicely flexible. In practice, it's kind of a bookkeeping hassle.
For all players, you can have your carnivores prey on your herbivores (so long as they're different species). This led to comments like "it's ok; I brought my own food to this biome". :-) A problem for carnivores is that not all herbivores are equally edible; some develop roadrunner DNA (speed, nocturnality, armor), and you have to adapt (speed, nocturnality, anti-armor) to eat. The carnivores end up moving around, following the prey, just like in real life.
The other thing that can make an herbivore inedible is size, and that was my biggest problem in this game. There are six sizes available in the game; a carnivore can eat prey of its size or up to two bigger. I had a gene that I really didn't want to give up that constrained my best carnivore to size 1, but Dani was going for size 5 and 6 creatures because there are places where herbivores compete on size. It's complicated but mostly good.
That trait I didn't want to give up? I think this was a huge factor: I got a poisoned bite, which allowed me to ignore roadrunner DNA. (I don't understand, logically, why it would help with speed and nocturnality, though helping with armor makes sense.) In a previous game when I was playing a carnivore strategy the prey kept hiding or running away; since DNA comes out randomly and then you have to win the bidding, addressing this isn't always easy. But this time the luck ran in a different direction.
For a while Dani and Alaric were doing better on population than I was, but I managed to catch up and ended up winning by about five points (with top score around 150). Alaric would have instead won by one point if the disaster on the last turn hadn't made one of his species extinct. Ah, fickle fate.
The game seems to work best when players can fall into niches, but that's not always possible and a fair bit of conflict is inherent in the game. I think it works reasonably well, but the 3-player game came in at 5.5 hours, a little longer than I expected. Each player and each species adds complexity, so I think we need to come up with some player aids (visualization, mainly) before we try another 4-player game.