Is room treatment a science?

I keep it simple: 1. Walk around your room and clap your hands. If you hear echoes, put something (I use foam panels) on one of the opposing walls. 2. Put panels on the "early reflections" areas close to your speakers (to kill the early reflections). 3. If the overall sound is unfocused, use panels until imaging improves. 4. If sound starts to sound flat or dull, remove some panels -try different combinations to see which sound best.
Also, try to avoid large pieces of glass (use curtains, etc.) -avoid reflections.
If possible, try to make the room symmetrical. Don’t have the left speaker projecting along a solid wall and the right speaker next to the dining room (open concept -no wall). try to make things equal on both sides of the sweet spot. So yeah, it's pretty much a science. But in the end, make it sound right to YOU. Good luck!

Actually trial and error is fast, cheap, and easy. Its what I did and highly recommended. Provided you do it the right way. Otherwise yes it can be incredibly expensive.

Dweller nailed it on the slap echo. Here's how to do it methodically, cheap, and easy. Do what he said, with OC703.

Owens Corning acoustic panels are industry standard. Thicker panels absorb lower frequencies but a couple 2'x3'x1" panels is probably all you will need. They are cheap and light and easy to cut with a box cutter. Here's a picture of my room from many years ago when I was still experimenting. https://www.theanalogdept.com/c_miller.htm Notice lots of yellow OC703 panels on the walls. They are temporarily held with push pins. That's how easy it can be. 

Notice the dark gray panels in the corners. Those are the same OC703 only cut to fit and covered in fabric. DIY acoustic treatment. Very effective but without making the room sound dead. 

Now here is more recent. https://systems.audiogon.com/systems/8367 No more big panels on the walls. Just the corner tunes. Much better! Its rare someone comes in my room and doesn't comment on the acoustics. Its not dead, not lively, but everything is crystal clear.

Acoustic treatment is a balancing act. I don't need side panels to catch the first reflection, probably because my speakers are more than 4' from the side walls. If I did they would be as small as possible, no more than one to two feet square. But this is why you buy the panels and experiment with them like I did. Its so easy you can't believe it.

That's the old school acoustic treatment method. Its great however only if DIY. Because the minute you talk about spending more than to buy a few cheap panels you'll get much better results going with something like Synergistic HFT. So start cheap, and build from there.

Yes.  Room acoustics is a science and is written about by much smarter and more accomplished people than I.  I like to read Floyd Toole when I want to pretend I'm smart.  Otherwise I ask GIK Acoustics for advice.

I will say after lots of measurement and experimentation that treating your room well is never a mistake. My room treatments have outlived everything else I own. It is by far more productive to treat the room than start swapping speakers, cables and amps. 

Great ideas!  The project begins. I thank you!