Finally they ditch spinning media on the base models. Also notable, the rumored iPad-like style changes are conspicuously absent, these look pretty much identical to the older iMacs. Otherwise this looks like a decent bump all around. Notably, the iMac Pro also got some love (though not too much it seems?)
If you upgrade the new 27" iMac to the same specs, you can get a faster machine than the base model $4999 iMac pro for $900 less - it's a faster clock speed 10-core processor, better performing GPU with Radeon 5700 XT 16GB (as opposed to Vega 64 8GB), and same 32GB RAM and 10Gb ethernet and 1TB SSD for that price.
The iMac pro has even further upgrade options that the iMac doesn't, but still, I wouldn't expect a $5k non-upgradeable pro machine like that to be underspecced. It'll also be interesting to see some teardowns of the new iMac and compare actual benchmarks between these machines, the iMac Pro might still have better thermals that lets the cpu/gpu perform better in the real world.