Up until the 70s, the efforts of home audio manufacturers focused on creating the best quality sound possible. Since then, the efforts of the mainstream have focused on making things smaller while adding more and more features. So now you can get something the size of a pack of cigarettes that holds months worth of music on it, lets you watch movies, make phone calls, check your email and so on. All that's fine, and I'd have an iPhone if Belfast was in the service area too. At the same time, I can't help but feel a little disappointed. For all the advances in technology, sound quality has actually gotten worse.
There are alternatives, though. There is the audiophile route. While most of the industry went towards making things flashy and small, a niche market of audiophiles have continued to try to make the best sounding equipment possible. So it's still possible to find audio equipment that sounds incredible, that will make you realize that the music you're listening to on your MP3 player is just a pale imitation of real music. There are problems with this approach, though. First, you have to deal with audiophiles. There may be some audiophiles out there who aren't elitist jerks, but I haven't met them. Secondly, audiophile gear is expensive. There are speaker cables that run into 5 figures! Of course, you don't have to spend that much to get great sound, but the problem that to determine what is inexpensive and good vs. what is cheap crap, you have to talk to audiophiles. Further complicating things are unscrupulous companies like Bose, who sell cheap crap at enough of a markup that the people who buy it think it's good. It's not. It's awful plastic garbage.
A much better alternative is to go retro. Keep your eye out at yard sales, pawn shops, flea markets and you can still find pre-80s stereo gear. I've found vintage receivers for $2 that blew away anything you could get at BestBuy for hundreds more. It was a very different design paradigm back then. Technology was an investment you expected to be using for decades. If something broke, you'd get it repaired. So pre-80s equipment can still be going strong, while we only expect to get a few years of use out of what we buy today. The reason that people put this stuff into yard sales is usually not because it's bad, or stopped working. They just want something smaller. But if you have the space for it, you can pick up something that sounds fantastic for a few bucks!
In general, when you're looking at old gear, there are two things to look for. As a rule of thumb, the heavier it is, the better. If you pick up an old receiver and it's heavy enough to warrant the "lift with the legs, not with the back," rule, chance are it's got some solid state equipment in there. Secondly, look for "real" materials. Things made out of metal, instead of metallicized plastic, or wood instead of laminated wood grain veneer, will sound better than things that aren't.