Jewel of the North
I don't buy many 5e products but most of the cover art, including Tasha's, I find really tepid. Of course, it's incredibly well done, but it doesn't excite me at all.
One exception would be the Ghosts of Saltmarsh cover, which I'm pretty fond of.
I noticed when I was flipping through the Art and Arcana book, the later art just seems to lack any charm to me. The early stuff is really goofy, but very endearing. The mid period is much better and I generally like. The latter stuff is very proficient, but it just seems boring to me. I'm not sure why exactly.
I would agree with you. The 5e art (like most of 5e stuff, really) is superbly effective: it just works and its really well done. But, its a little dull. Like, in 20 years, I'm pretty sure I'll still remember some specific pieces of pre-5e editions art, even some from edition I never played, but I'll just have a vague memory that, in general 5e was good, but without lasting impression. Anyway, time will tell.
Strangely, while 4e had the most boring presentation of content, I absolutely adore the semi-over-the-top art. Without being really well done, they were evocative, with is a requisite to give a lasting impression IMHO.