I am really pleased with my G5 iMac except for the sound from the internal speakers
It really is nowhere near as good as it was on the G4 or even the G3.
Although it's very clear, it does not go loud enough.
It's OK for personal use, but I have used it on the G4 in the past to play music in the room I was sitting in. It is not loud enough for that on the G5, no bass either.
It's not a problem for me now as I use an Airport Express unit, but it's worthwhile knowing that it's a much quieter sound system than the G4.
The iMac G4 had an 18 watt amplifier, but the G5 only has 12 watts, quite a drop in output.
If you need the G5 for sound use then consider external speakers.
Ian