The G12-65 has a good all-round frequency response with a slightly over-eager top-end response. Clean sounds are clear and crisp. The bass is tight and not at all boomy. Although there is a small mid-high peak, edgy sounds break up nicely with some fizz in the higher registers, while the bass remains intact so that power chords don't get muddy. Although it can sound smooth and warm, it leans slightly toward creamy-crunch when pushed. It is capable of producing drive and distortion tones ranging from thick and woody (Eric Johnson, Cream) to sharp and searing lead. For my taste, it has a tendency toward being slightly too bright, but it never gets ear-piercing in any way.
It took about ten hours to break in the speaker. I've gigged with it for several hundred hours now and it's holding up nicely. It is mounted onto a birch plywood baffle attached to a pine plywood body, which is quite ideal for isolating the sound of the speaker. I haven't methodically tested it in various speaker configurations such as 2x12 or 4x12 and have only powered it using a couple of different Mesa Boogies and a Dumble. It provides a rounded bass response for when I'm playing clean jazz. It gives me the required treble for funk, cuts through nicely for country lead and blue grass, and it sings really well when I'm playing blues or fusion. In challenging gig situations, I need my tone to cut through but not to get too rude and ugly, and this speaker is well suited to these requirements.