Interesting video on voting systems https://www.youtube.com/watch?v=3Y3jE3B8HsE
So if you prefer Owl > Gorilla, you still have to go with Gorilla as #1 because Owl might not have enough to beat Tiger. This means it still leads to Tiger vs. Gorilla two party system.
It's already implemented in Australia and they still have a two party government.
Here's an example here:
http://www.electology.org/#!approval-voting-versus-irv/c1mmu
With IRV Obama would've crushed all of his competitors when he got elected for the 2nd term. IRV seems to favor incumbents greatly, which is probably why things haven't changed so much in Australia either - so not much better than FPTP in the US. People still very much vote strategically with IRV.
With approval voting on the other hand, Stein (Green Party candidate) would've had a huge chance in the election. Maybe she would've still lost, like the chart predicts, but we would've had much better kind of debates than Obama vs Romney.
Romney would've been crushed because he was so disliked. In fact many other "fringe" candidates that were liked in that election would've done much better under approval voting than under FPTP or IRV.