First Mac after moving from PC. Love the machine, it is great to look at, fast and coming from a PC - quiet. Fan only comes on when I play the only game I play - Civ 5 - and fan noise is much quieter than I am used to. Mostly though the iMac is silent for me.
I have i7, 3TB, 295, 16GB RAM. Hope to get 3 - 4 years out of it.
Just a not on the longevity of the iMac (from a former PC user):
I got 6.5 years from my early 2008 iMac, with 6GB RAM (It is still running, and the kids use it for their games). In that time, I have had the following "bumps in the road":
1. Graphics card failed. Apple wouldn't touch it because I upgraded the hard drive (twice - once from 240GB (?) to 2TB, and the second time to replace the 2 TB drive, which was failing. Replacing the HD is like this: Remove the HD, put the new one in, boot to Time Machine Restore, wait. Done. The only product that wanted keys was Office)
2. Wiped the hard drive clean (like a fresh installation of Windows I used to do every 6 months) and reinstall. Time Machine is a true wonder of the world! Pulled the data files from the hard drive, and had all of my documents. I was worried about reinstalling whatever made the Mac slow with the TM restore, so I did it manually.
Having said all that, I am very happy with my decision to try out a Mac 6 1/2 years ago, and while the initial Out of Box Experience was rocky (Finder is like Program Manager from Windows 3), it's solid, fast, and beautiful.
As for my Retina 5K iMac (maxed out, 3TB Fusion Drive), I LOVE IT! Play Lord of the Rings online, and it's fast with the highest settings possible (no 5120x2880 - Program Limitation). I run virtual machines on it, and there are no issues with heat or fan noises.