The best antidote to an untreated ,bad sounding room, is to invest in a good set of headphones and a good headphone amp.
In fact I'll go so far as to say, that anyone who is seriously thinking about making component upgrades,should invest in a good headphone set up first.
A lot of people trade one colouration for another and as good as some DIY attempts at room tuning can be( I'm a DIY room tuner, but far from great)most times if you don't know what's on your cd or record in the first place, you'll never know if adding a ton of acoustic fabric has done more harm than good.
Then again, there are other options for the folks who don't have their own dedicated listening rooms and are at the mercy of their wives.
Try some room correcting audio black boxes.
Lots of them out there , some are quite pricey,but some are now being built into two channel integrated-re Harmon Kardon, so all hope for better sound is not hinged just on how many(if any)absorbing panels and tube traps the wife gives her consent to.
The refernce to headphones was meant to illustrate what our gear can sound like when the room is taken out of the picture.It's not to imply that what you hear thru the phones is perfect.It's also coloured, but the colourations are not those of the room.
It's just somthing to compare when you start down the room tuning path.
If the life is sucked out of the cymbals and you've lost any sense of the air and life around the instruments compared to what you hear thru the phones, then you'll know you've added too much.
And just as you can have too little room tuning, you can also overdo it.
I have followed a lot of the tips from the Master book of acoustics by Everet,it's a great place to start.