i would say
best install a app like istat pro or smc fan control or fan control so you can see the actual fan speeds , because LOUD is relative and not really a clear indication if something is normal or not as the fans are at about the same hight as your ears and direct in front of you , but that is absolute normal on a "all in one" and human ears have the tendency that they are not calibrated in all humans the same way ,
for some a fly is annoying loud and they cant sleep ,while other who live since years near a military airport think a tornado at takeoff is quiet
but despite the iMac has a i7 CPU and a moderate GPU its capable to run most games at moderate settings, but its just not a gaming rig, its a Mac