A tinge of sadness. I remember reading reviews of the X-25 like a decade ago and being so excited (it was this anandtech review https://www.anandtech.com/show/2614). To me it was the dawn of the "common SSD". Just now I've looked at a bunch of timelines of SSD history, and I suspect the X-25 was similar to many other people. There was certainly a lot of SSD activity prior to the X-25 being released, but it seemed like the only customer facing brand that had an offering before it was OCZ (you can see it in the review comparisons... you can also marvel at the old 10k RPM HDDs... how's that for a nostalgia trip).
Intel pretty much stopped being relevant to the consumer SSD market as soon as the SSD market as a whole broadened enough to support the development of client/consumer-specific SSD controllers. Once Intel could no longer compete by stripping a few features out of an enterprise SSD design, their consumer SSD products had no real advantage over other brands. (Minor exception: Intel's consumer QLC NVMe drives have consistently had very good retail prices.)
If you mean the 660p/665p, I think even those SSDs are not worth it. The Kingston A2000 uses the same SM2263 controller, is about the same price, but uses TLC NAND instead of QLC.
Oh totally. By the time I actually had my own money to buy an SSD (so like 2013 or so), Intel was completely out of the running (I went for a Crucial). As you said, I remember looking at some reviews last year and being surprised that Intel was in the running at all in any category.
Intel pretty much didn't design it. It wasn't worthwhile for them to invest in making a consumer-oriented NVMe SSD controller of their own. Instead, they used the first NVMe SSD controller from Silicon Motion, whose SATA SSD controllers Intel had been using for a while. That SM2260 NVMe controller was cheap but bad, because it was made on a 40nm process (compared to 28nm or smaller for most NVMe controllers) and it was Silicon Motion's very first NVMe controller so they had lots of bugs.
