so does turn 3 special on Reaper = win?

[Emuchu]

Reaper is an unusual map in that there are a LOT of very powerful P1 strategies that can be employed by each team, as you said.

It takes a lot of metagaming to be successful as P2, but the good thing is that many of the P1 rush strategies have a "tell" (such as unusual Runner placement or a delay in taking the Wit Space) as well as a hard counter. I recommend you find a training partner and drill through the common P1 Reaper openings, especially the intensely speedy Mobi and Scrambler variants, as it takes quite a few tries before their subtleties become apparent.

One such quirk is the precision of the opening layout: most rushes must deal a very optimized amount of damage by moving the pre-deployed units and managing spawns and Wits in very specific ways, meaning that, for the most part, you have a very good idea of what your opponent is about to pull and can try to counter it. In the Titan league, Reaper matches have become insane poker mind games where both sides try to mislead the other into making a single mistake which costs them the game!

The short version: For every hyper-optimized P1 opening, there is a hyper-optimized P2 counter for it, but the hard part for BOTH players is guessing whether his opponent has the correct plan. Sorry to say it, but this is probably the top map to practice openings on (and Foundry, I suppose).