Oh, there's a lot that has changed... I would like to know about others' opinion as well!
Old for me is 2011-2012 and before. That is where you can clearly see the difference between the older and newer ones.
The problem with many new dramas is that they are no longer consistent. They try to match interests of different types in a single drama, as if to catch as much attentions as possible. Therefore, they fail in taking us with them to their consistent world. Mixing genres doesn’t always work (sometimes only though).
Also, the OST no longer feels like it was tailored to a drama like before, in most cases. Yes, the songs might be good, nice, and catchy, but not like it came naturally or born out of the drama like before. I don’t like the OST only because they are good, I like them because they remind me of the feelings I had while watching the drama
At first, I thought that it was because I am older, I no longer felt like I did when I watched them back then. But I discovered that that wasn’t the reason, and I proved it when I recently watched older dramas that I never saw and I felt like my old self did.
It feels like they focus too much on visuals. It is overdone nowadays, and it affects the quality of the overall experience badly.
I have also done this using MDL's cool advanced search:
The ratio of fantasy/ supernatural dramas to non-fantasy dramas increased from 1:100 ( before 2012) to 20:100 (2013-2020)
Which is from a barely 1% to a whopping 16.6%
that is if you compare the number of fantasy/supernatural dramas with the non-fantasy/supernatural in the years before 2012 and 2013-2020
This makes newer dramas less realistic
I am not sure about this, but I think older dramas took their time, where new ones can be both slow-paced or fast-paced ones.
Of course I am not criticizing all newer dramas, because you can actually find those that engulf you completely and make you unable to escape, but they keep decreasing every year, and they are very, very rare.
And there are some recent dramas that have gotten very creative and brought us to new worlds. Those are the dramas that managed to truly develop and not just look 'modern'.
I also think modern rom-coms are better than older ones and easier to find, but serious dramas were best back then.
edit:
I forgot about slice of life, one of the genres that I really like, it was almost non-existent in the past.
edit 2: forgot to mention I have only seen k-dramas so far