Is it normal to have to tone things down in post after shooting with a circular polarizer?

So I got my first ever circular polarizer recently, and as it was sunny this weekend, I went out back, aimed 90 degrees from the sun, and shot two images--one with and one without my new B&W filter. This is in M mode, ISO100 and adjusted the shutter speed to be right in the middle of what the camera thought was the correct exposure at F2.8 (speed was something like two or three clicks slower with the filter on). I'm VERY pleased at the extent to which the filter applies the desired effect...but if you look at my test shots, the one with the filter is very near being too contrast-y and saturated. Also, the greens seem to have shifted a bit.

Now, I'm sure with some proper testing and more experience, I will learn how to use this filter appropriately and in the correct situations. [And yes I know the test shots are not properly exposed--I just wanted to keep things the same regardless for comparison purposes]. However, I'm curious if, before I start off on my journey of learning how to use this, I should expect to have to make some adjustments in post no matter how good I get with it.


Thanks for your comments...