Is the ISOCELL any good?

It very much seems to be mostly numbers but it really can't back up the claims in actual visual image quality. The noise and required light to get anything near good shots is very high, the DOF on such a large sensor is downright tight, which is nice for making pretty looking shots..but really bad for just someone trying to capture a photo. Even on the S20 Ultra taking a photo of a person from 5 feet away results in the nose and eyes being in completely different focus.

The fact of the matter is that in normal use, a medium format mobile sensor with a moderate pixel count is preferrable. (I.E. iPhone 11 Pro, Pixel 4) as for 95% of shots you want a wide DOF to put all of the content in focus and great per-pixel aperture to reduce exposure time and ISO so you can reduce camera shake and Noise. Even in the shots you want DOF (Portrait), faking it tends to lead to a more adjustable shot where you can correct after the fact instead of being actually stuck in a inch-wide focus gap where any movement of the camera or subject results in out of focus capture.

Plus most photos are posted online in the 1-2MP size. Now cropping is a great extra 5% item, but for those who want really great photos they would have a lot to gain from a much larger sensor with a larger lens and lower MP count to get way less noise and better exposure times (I.e. The Sony A7R IV) Whereas dedicated full-frame equipment just trashes mobile results.

We went through some “megapixel wars” in the past and it turns out, like you said, there are a lot of tradeoffs here and optimizing for high pixel count means you have to make unacceptable sacrifices elsewhere.