Actually, flat.

A learning curve usually is time on x-axis and knowledge-percentage on y-axis. If knowledge-percentage only slowly increases the curve is flat. A nearly vertical curve means you learn fast.

This is a little bit like educating people about kerning [0]. For another example, a "quantum leap" is basically the smallest possible leap you can do.

[0] http://xkcd.com/1015/

I always assumed the "learning curve" is the curve required to make progress in the game, i.e. the x-axis is "progress in the game" and the y-axis is "knowledge-percentage".

Most learning curves I've seen actually imply the reverse, with time on the y-axis and knowledge on the x-axis.

In that case, a learning curve is a sort of visual hill with a steepness indicating difficulty of progression.

Or if by vertical he means running face first into a wall...

Upvotes for both though...

It's a wall with electrified spikes on top. And armed guards instructed to shoot on sight. And rabid dogs. And behind the wall there are other walls.

I tried to start the game 5 times. The first 3 I could not even start a game. The 4th one I followed a tutorial and was able to start, and nothing else. The fifth time, I found Captnduck's excellent video tutorials ( http://www.youtube.com/watch?v=koZUS2h-Yzc ), and I was finally able to break into the game.

Then they added a whole layer of complexity to the military (with a lot of new UI quirks) and I just stopped playing.