1. Price
It's weird to see that the iMac, with the same internals, is $300 more than the MacBook Air. Sure, there's a fan and a bigger brighter screen, but since when has an equivalently specced laptop been cheaper than the desktop version? Twenty odd years ago, the iMac was $1,299, and the comparable PowerBook G3 Mainstreet was $1,999. Now, I don't expect that gap to exist today, but I'm definitely surprised they went with the custom screen and higher price, when an EDU/Institution focused model could easily have shipped with a decent, non-Retina 1080p IPS display for $999... or even $899.
2. Specs
These are, like the 21.5" iMacs that they're replacing, non-upgradeable. In fact, they're even less upgradeable, as the 21.5" models still had the option to upgrade the hard drive, if one were so inclined. A desktop, starting at $1,299, in 2021, equipped with 8GB of RAM, looks under specced at the least, and worst case scenario will underperform badly in a year or two with new OS and software. I understand for an entry level institution focused model, but the midrange, at $1,499, is shameful.
The inclusion of two TB3 and two USB-C ports on the midrange also makes one thing very clear - the M1 likely doesn't have the IO to support four TB3 ports. On the Mac Mini, this was masked as there are only two TB3 ports, with the remainder being USB-A style ports. If Apple couldn't put more TB3 ports in for technical reasons (or reserving that for an M1x), I think Apple ought to have maintained that USB-C/USB-A split on the iMac, as well. A UHS-II SD card slot wouldn't hurt either, especially as the internal drive isn't replaceable.
3. Design
I honestly don't care about the colors, or the bezel, or the chin. No, what I'm disappointed in is the fact that they decided to go in the direction of thinness-above-all. A slightly thicker iMac could have had quite a few possibilities - the one that's top of mind, for me, would be a fan-free model. A thicker heatsink, with 'ventilation shafts' coming out near the top, could allow convection cooling, not unlike the iMac G3s of old. A completely silent iMac would be fantastic for libraries, recording studios, and other instances where even a little bit of fan noise could be distracting or unwelcome. If the M1 can be fan-free in an MBA, it can be fan free in an iMac. A thicker casing would also have allowed for USB-A, as well as a headphone jack that's not on the side - which might be fine for headphones, but a little unsightly if one were to plug in external speakers.
4. Keyboard (personal pet peeve)
This, admittedly, is very much my thing. I don't like the rounded corner keys, and I really, really don't like that the arrows aren't in an inverted-T layout on the non-extended board. The left and right arrows don't even half to be half height - make them 3/4 height. Or put little nubbins on them like the F and J keys. Something that I can use to position my fingers without having to glance down.
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Those are my major reasons for not liking the iMac. I'll have a need for a mostly sedentary machine in the next few months, but if I can't upgrade a desktop, nor save much money on one, why wouldn't I just grab a laptop and have the portability if needed? The iMac appears to have almost all of the drawbacks of the 13" MBP (too few ports, too little RAM for the price), with few of the benefits of a desktop (higher performance, upgradeable RAM/HDD, lower price).
