Is room treatment a science?

Yes, it’s a science. Reading the books and asking experts is always a good approach.

A few easy tips:
- “ slap echo” just means clapping your hands in center of room and
     listening for echo.
-if a ping pong ball will bounce off a surface so will sound.Glass 
 sucks.
- wool rugs work.
- book shelves on side walls with uneven books break up
  waves and work.
- try closing doors.

You can probably get a reasonable result that you are happy about by simple self administered methods or you can spend money up front and get an audio guy (they are normally involved with setting up home theatres) to come in and analyze the room for you.

The latter would certainly cost more up front, but would also prevent you trying things that didn't work, going down dead ends and spending money on the way. hard to know which would work out better and cheaper.

Many sophisticated descriptions of acoustician principles.
My main system is in my family room and my wife would never agree to have panels and other acoustic treatments on the walls!
I have experienced room treatment as extreme as a half million plus spent to create a dedicated room with acoustic walls floor and ceiling! For me, the most WAF friendly and very effective treatments are ASC products. Their bass traps are elegant grey cylinders that can be placed behind to the corners of the speakers. I don’t have them now but have used them in the past to great effect in focusing the sound and tightening the bass.

a lot of good advice above. I built  28 x 17 room from scratch with acoustics in mind. I wanted only minimal wall treatments. +1 on ASC tunable cylinder traps. very versatile and effective. trial and error will definitely get the "low hanging fruit" and produce a noticeable difference. but it is a science to clean up a room while keeping it lively.  I had my room tested and identified resonant frequencies and where they existed.  Placed absorption & diffusion treatment as needed for the specific problem frequencies. I had everything tested and made through Artnovion. Color & design coordinated with room so it looks beautiful in addition to sounding great (to me). I think a good room treatment is like upgrading every component you have at once. Good luck 

There are many good responses explaining the science and approach to this problem.  So I don’t have anything unique to add.  I do highly recommend you look at the Acoustic Sciences Corporation (ASC) products.  I have used them for the last 15 years.  They have traveled with me to three different houses, five different listening rooms.  The ASC Tube Trap is simple and elegant.  Each Tube Trap is designed with an absorptive side and a diffusion side.  This is important in that the solution for tuning a room is not always absorbing unwanted reflections or frequencies.  By using a combination of absorption for removing unwanted bass reflections and diffusion for addressing mid and treble frequencies you can create great focus in the room, while still creating a sense of size and liveliness.  Good luck on your journey.  Cheers!