Sure, Hearthstone has always had that element since the GvG days, but I feel like they are going a bit too far with it and I am genuinely starting to feel like I should be handing my card collection to my 4 year old nephew. Seems like it's more catered for that demographic.
Even just comparing the new versions of the dragon aspects.
I see your point. And I valuate that you bring this up. The artwork has clearly changed. But imo a lot of the cards are looking really good, even though there are exceptions ofc.
I think the art of Ysera the Dreamer is truly amazing. Very majestic. And the art of all the "new" Old Gods are amazing. These are just a few examples, but my point is that I don't think the art have changed to be worse, just different.
The art style has been the same for many years, I agree with the cards that you listed. The new dragons look really generic and boring. Though, in a way the art style sets hearthstone apart from other card games like LoR or Magic. I think this is an important reason why hearthstone succeeded, and the original WoW cardgame failed. Hearthstone is aimed at a casual audience, while most card games aren't.
I do agree however that some cards, like the ones you mentioned, took this a bit too far.
Different artists will produce different art. This is true. Within the same set, you will have some that look especially silly or cartoonish, and some that are very realistic. I think this is part of the charm of the game, to have varying styles presented.
I think overall, there is no card art that looks especially bad, to me. But art is also subjective, so I doubt there will be a concise and unanimous response to this question here.
Hearthstone always had some "silly" artwork in the past, as it still has more "serious" artwork in modern expansions.
I will concede that in quantity, there are more cartoonish or "cute" cards in modern expansions than in the past. Not a surprise though, as the game is actually intended to be more on the silly side, and not a perfect card-based recreation of the source material, like you have it in Gwent or TES Legends. It might also have to do with expansions themselves being generally more lighthearted (to varying degrees, of course).
I also see that newer cards usually have less contrast, but I can also see why the developers might prefer bright colors, when the cards are already a bit small in the game. When the artwork is too dark, going for a realistic look, it's also harder to make out the details on screen. It needs to be mentioned that older expansions commonly recycled old artwork, while new sets (well, "new" like since Old Gods) usually have completely new artwork.
I can see what might bother you. Still, your examples are cherry picking, and I could name dozens of newer cards that are not on the silly side. I can't argue with your impression, but it feels you are little unfair, and mostly upset that artworks featuring prominent characters are not matching your preferences.
Keep in mind how subjective the topic is. I know someone who had the exact same sentiments already during Descent of Dragons, that all the dragons would look "chibi" (yes, he seriously said that), and in all honesty, I can't even begin to figure out how Murozond the Infinite or Deathwing, Mad Aspect aren't enough "badass dragon" for you. Bright colors, but especially with Murozond, I think it actually enhances the otherworldly vibe.
I am totally with you, that art is an important part of video games, but even if we say that Hearhtstone has changed substantially, it's a different question (and probably comes down to taste) if it really has changed for the worse. Personally, I'm fine with it still. There are some artworks I like, some I don't, in every set new and old. There's enough variety that goofy gnomes and the like don't irk me. And there are only very few that really bother me.
Either way, I wouldn't discuss this in terms of "quality", because quality usually means craftsmanship, while you are (I assume) mostly lamenting the style, like the intensity of colors and shades, or the cartoonish look. But darker pictures are not automatically more sophisticated. If you don't like it or like is less, that doesn't mean "art quality is suffering".
I really like Hearthstone's goofy and colourful art style, it goes with the fun voice lines and pop cultural references, another thing I really enjoy. I don't particularly like the new dragon art though. To me, they really stick out from the rest of the art, and not in a good way. They have a strange 3D effect, which almosy make them look like figurines.
The flavor of the expansion influences the style of the art. With more "fun" expansions, you get more whimsey in the cards and their art. With more "serious" or dark expansions, you tend to get grittier, more detailed/dark shaded work.
Watch Ink Masters some time and check out how different artists approach different styles of tattoos using their own style. If you have an artist that is highly skilled at traditional Japanese, and you ask them to do an American Traditional or New School style tattoo, you are going to get it because they are good, but you are also going to definitely see their own flavor blended in.
Card art is no different. No other art is different, really. It's art. It is subjective, and comprised of many factors, not the least of which is the artist, the subject, the theme, etc.
I like the art in the game, myself. It strikes a balance between the cartooney and the serious in just the right places, more often than not. You can tell that the development team cares about their work because the voice effects almost always match up with the artwork perfectly.
When I look at the old vs new Dragon Aspects what I think of is that the old ones are drawn to appear as forces of nature. their bodies are ill-defined, and they are wreathed in power of the color of their aspects. truely the definitive version of those characters.
in contrast the new ones remind me more of something you'd see in Yu-gi-oh. Magestic Dragons, usually in the middle of attacking with their signature attacks, and showing off the full silhouette and stature of the monster.
I have to wonder if this change isn't even just because of Hearthstone, but also the progression of WoW in general. if you recall the first few expansions we got were all from early vanilla WoW-Wrath of the Lich king. back then all give aspects were still alive. they seemed like immortal, eternal forces of nature that would never die. but as of late that has been less and less the case. first we killed Malygos in late Lich King. then Deathwing in Cataclysm. Ysera in Legion, and Norzdomu in timetravel events. maybe the reduction of the aspects from primal forces of nature down to "big dragons" is appropriate for the age in which the Warcraft Universes exist in now.
I do think the art, sound, and feel of hearthstone is the biggest reason I stick with it instead of playing Legends of Runetera or Magic. LoR just feels too queit and I miss my "go ahead, make my day" from hearthstone, and Magic Arena feels too still, like I am just playing tabletop simulator.
but I guess it does say a lot that my favorite legendaries are all still classic legendaries, at least when thinking art+sound. King Crush is the best summoning animation. followed by Deathwing
Agreed, this new art direction over the past few years is way too childish in my opinion.
One of the reasons I will stick primarily to classic is the old art which was more sober and mature. Look at Ancient of Lore, old Alexstrasza, Grom, Krush, Cenarius, the old Deadly Shot arr, very good art for more mature audiences.
Odd that more players are not talking about the shift in direction of card art to child Yugioh style.
As implied earlier, the art style has (as I see it) gone from a MTG like drawing style to a more "cartoonish" style. Maybe this has been done slightly on purpose, given that the "quality improvement" of WC3 reforged was a fiasco and by some called "Chinese phone game style". In other words, Team 5 might want the game to stand out as a Warcraft game. Or they just try to save money IDK.
The themes are another thing IMO. TGT was arguably the most childish and jesting expansion of them all, but the drawing style was still more MTG/fantasy book-like. That DMF and Scholomance both have a very warm/jesting theme is more coincidental I think. AoO seemed darker and more WOW oriented than the whole past years expansions. With a touch of Mad Max of course ;)