I don't know how to answer that since I haven't watched TV for three years, and I didn't watch a whole lot from the mid-'90s onward anyway. Supposedly the quality has improved a lot, at least starting with The Sopranos, and running through today with Mad Men.
I've never seen those, so I'll just accept that they're very good TV shows. Still, that does not mean that the average show is better -- maybe there is only greater variance than before, resulting in a lot more shows at the great level but also a lot more at the garbage level. From what I did tune into during the 2000s, I definitely got the sense that there's more garbage -- lots of new, boring game shows that started with Who Wants to Be a Millionaire? and lots of nauseating reality TV shows.
As recently as the 1980s, game shows were still mildly entertaining rather than stupid -- The Price is Right, Jeopardy!, Press Your Luck, the goofy slapstick of Supermarket Sweep, etc. The only reality TV back then was Lifestyles of the Rich and Famous, and everyone's reaction was "gag me with a spoon." The first three or four seasons of MTV's The Real World (early-mid-'90s) were OK, but it already started sucking by the Miami season of 1996. I only checked in on it intermittently after that -- Hawaii in 1999, Paris in 2003, and Austin in 2005 -- and it got worse every time.
I also don't believe that there are more high-quality shows now either. The two that always come up are The Sopranos and Mad Men, and perhaps there's another one or two at that level. But that's over the course of a decade. I can find three engrossing dramas with great writing from a shorter period of the late '80s / early '90s -- The Simpsons, The Wonder Years, and Twin Peaks. Maybe throw in Tour of Duty too. The 1970s had All in the Family and M*A*S*H. Perhaps the new TV shows that get so much attention fill a previously uncolonized niche for content, look, dialog, or whatever, but there were just as many (maybe more) TV shows that had the same overall quality level.
And that's just TV for adults -- don't even start me on TV for children. With my 2 year-old nephew home for Christmas, I had to sit through a bunch of episodes of the Alec Baldwin phase of Thomas and Friends, as well as Spongebob. And it was just as bad during most of the '90s with Barney, Teletubbies, and the dork patrol that took over Nickelodeon (Doug, Rugrats, etc.). Fortunately the Netflix streaming service has the first season of Inspector Gadget, and my nephew went nuts over it. He began dancing to the catchy theme song (impossible with Thomas or Spongebob) and spontaneously kept imitating the voice of Dr. Claw while making a menacing posture (he never imitated the dweebs on those other two shows).
Pretty soon I'll get him the DVDs for Bravestarr, a well written Western set on an outer-space frontier mining town. I started watching Jem on YouTube, and it's more exciting and has better writing than the kids' cartoons of the past 20 years. But my nephew would never watch a girls' cartoon -- hell, neither did I back when it originally aired (although I always tuned in long enough to take in the Pat Benataresque theme song).
And no educational programs today try to make learning fun and cool for children. Bill Nye was all right but too gee-golly. Beakman's World drew us in with its Beetlejuice / mad scientist appeal, and Mr. Wizard's World fascinated all young boys by showing us how to set off a bottle rocket in our back yard, set stuff on fire in the kitchen, and instantly crush a thick metal jug using the different pressure levels of very hot and very cold substances inside vs. outside the container.
Getting back to the main point, it's not very hard to find as many or more high-quality shows from earlier times as from the past decade, and it's easy to show how much more garbage there has been piling up on the lower end over the past 15-20 years. If anything, it looks like TV has gotten worse.