The G3’s have Mega Imaging if you’re looking at the DI or SI versions. It’s a “clearer” picture on both. I would imagine there are some other features that separate the two units but that’s the big one.
I have a G2 SI and a G3N CHIRP which is just the 2d. The “N” in the name just means it can be networked to another unit or trolling motor.
The g2 helix 9,10 & 12 si has mega side and down imaging.
The g3 just gives you a better mega picture out wider and a little deeper.
The g2n mega units kinda struggle to get a good mega reading On the side imaging In anything deeper then what I’ve found to be 33ft, Then you have to switch frequency to 800.
The g3 also extends further to each side on the side imaging then the g2.