Are you happy with your purchase? Any regrets? Wish you had upgraded the CPU, SSD or ___? What about fan noise?
About 2 weeks ago I purchased a top-end 21.5" iMac with stock i5 processor from the Christiana Mall Apple Store and took it home. It was a replacement for my wife's 2011 MacMini base-base-base i5. She thought her Mini was fine, but I thought it was slow (everything beach balled for 2 seconds when you clicked), and she didn't have a good screen, so it was an overall update for her--about time. The new iMac is purportedly 2-3x faster in benchmarks...
AND IT'S NICE.
The 4K retina screen is mind blowing, if you are coming from a $129 1080-cheapie monitor. She does art and video, primarily. For her needs, it is screaming fast! High Sierra and the fusion drive work well. The fan never runs enough to notice, frankly. It's a quiet machine. The speakers aren't the greatest, but they are fine. It cleaned up the desk area well and has excellent color and brightness. I don't think she regrets it one bit.
I have a top-end 2012 MacMini w/1TB SSD inside + 512GB original SSD, currently, and thought of upgrading. The problem is that the iMacs are SO nice now, but the improvement on speed and ability wouldn't be enough to warrant the expenditure.
My plan is to wait for the 6-core Coffee Lakes next year, probably the Cannon Lake or even Ice Lake beyond. Those will probably be dream computers for me. The 2012 i7 is still hearty, but I want a better screen and some oomph! for layering tons of instruments in Komplete/Logic Pro X, to create a huge and vibrant orchestra setup. The reduction to 10nm will probably cool everything down as well, and the Ice Lake processors will probably give me 3x speed and ability... but it is a longish wait.
The current iMacs are completely brilliant for medium-level CPU/GPU work. Depending on your needs, they might be slow--for massive 4K video works or huge audio work, CGI work, etc.
Hardware for Macs will reach a sweet spot in a few years when DDR5 comes in, everything is USB-C, and various hardware improvements are added to the reduced architecture. What Apple must do now is improve all software! Especially the MacOS and Siri and iTunes... not sure they need to improve on their "iLife" suite that much.
If you are a low-end-ish user, iMacs are "all that" at this time.