This brings up a lot for me, as an iMac owner who had a lot of unfortunate experiences, so please excuse the tldr!
Firstly, re the talk about the choice of a 5,400rpm hard drive. I don't have a 21" model but my 27" 2010 iMac is one of those that came with the noisy Seagate 1TB hard drive that makes the iMac sound like it has a noisy bass rumble stomach complaint. I'm told the 2010 21" models had the same problem, or at least some batches had the problem. If you are used to very quiet iMacs, it was no laughing matter. After a very long period of complaints, Apple finally issued a recall to replace the offending drives. I'm told they replaced them with slower spinning laptop drives. I'm not sure how they mounted them, perhaps with softer silicone grommets, I would be interested to see.
On past experiences with other repairs of (non Apple) hardware, the idea of a hurried tech opening mine and possibly marking or putting dings in the gorgeous Apple iMac case, had me replace the Seagate with a 2TB desktop Seagate model and some soft silicone grommets, instead of the iMacs fairly hard rubber ones. I am a qualified AV tech and the 2010 model iMac's glass is not glued in, comes off with rubber suction cups, so it wasn't a difficult replacement, though you have to be very careful with the ribbon cables when removing the panel with a torx tool. Not a job for the impatient or anxious and as there are no guarantees that your expensive iMac would work after reassembly, I can't recommend people do it. The 2TB drive, even using my soft silicone grommets, was still audible, though, if thankfully less so, but I wanted to retain a high capacity HD and at that time there wasn't a lot of choice with laptop-sized 2.5" hard drives, so in addition I fitted an SSD. I put the Apple-Seagate 1TB in the Seagate caddy that I removed the 2TB Seagate hard drive from. It works perfectly well as an external drive and, perplexingly, is comparatively quiet compared to my other external hard drives.
Unfortunately, the iMac's screen developed a stain/streak down the right hand side, another known issue with some of the 2010 models, which I read is a screen fault from the heat. The stain is liveable with but annoying. I installed a third party app to make the fans come on earlier when watching movies, etc. Though that model is designed to run hot, I wish I had gone with my instincts and fitted third-party fan control earlier. It halted the stains spread.
The supplied Magic Mouse failed shortly after the warranty expired, only the top surface works, the laser no longer does. I am trying to find a way to use the top surface as a trackpad but haven't yet found an app that allows the cursor itself to move. Also, you have to move the batteries around a bit, sometimes, because it drops connection; it is worse with rechargeable but even with Duracells I had to do that, occasionally. The tin foil mod helped make for better contacts.
I had both the supplied bluetooth keyboard and and the wired full length one. The full length one stopped worked shortly after the warranty expired. Fair enough, keyboards fail but I am used to being able to repair things and even once you get the top plate off, the internals are apparently riveted together, rather than using the tiny screws that my old white plastic Mac keyboards use, which I have been able to keep going with occasional repairs. The bluetooth keyboard still tethers with the iMac but... none of the keys work.
So, not a great iMac experience. I accept I was unlucky and whatever maybe said of the new iMacs, the new screens are particularly stunning, the iMacs cases are stunning and the lower heat generation from the more energy efficient parts in the new models mean heat is less of an issue, these days. The iMacs have very much come of age. I wouldn't be unhappy with a 5,400rpm hard drive, quietness wise, but to not be able to easily fit an SSD, because the glass of the screen is glued in place, wouldn't make me happy, at all. I think it's a pity Apple didn't dispense with the 5,400rpm drive and just fit a 250GB SSD. A lot of people would have slagged them off for the low capacity but trying to keep the costs faintly sane, it would have made perfect sense to me.
I am very glad to read that Apple went with Broadwell for the 21" Retina model; the Broadwell part's Intel HD 6200 graphics part is no slouch, absolutely destroying AMD's desktop APU, an impressive victory for Intel after years of complaints about Intel's puny integrated graphics as compared to those AMD A10 APUs. I feel a little sorry for AMD who had a nice niche going with their powerful integrated graphics, making for great small form factor PCs. Reading that the memory is soldered in place in the 21" Retina iMac, forcing customers to get the maximum about of memory at the time of purchase, if they want 16GB of memory, is wince-making but I appreciate that soldering in the memory keeps costs down at the time of manufacture. Still, it adds to that whole negative image of you are locked out if you want to upgrade.
Would I recommend iMacs to friends? Absolutely, yes, a hack mac and an all-in-one iMac remain, by form factor, are of course very different beasts, and those Retina screens with HD content are jaw dropping. The prices are a bit of a gulp, if I can see why they are the prices they are. I inherited my iMac and couldn't even remotely afford a new one. Also, I want to get back into video editing, so need more power and maxed out memory, Thunderbolt 3 is very appealing to me, a couple of M.2 devices as well, when I can find the money. I can forgo a Retina screen, while still knowing that I am missing out, a bit. There are some expensive aluminium PC cases that I like but... There's nothing looks quite like an iMac.
