Yes, it's a great idea to trade for the Z2! I owned both the G3 and Z2 at the same time and ended up selling the G3. I came from a G2, which I loooved, so I really wanted to like the G3, but it just had too many flaws. The G3 is way too laggy. That's my number one pet peeve. If a phone feels/looks slow then it IS slow. It was fast within applications, but transitioning into apps and back to the home screen etc. made it stutter a lot. Also, the high pixel density screen is just a gimmick. I'd gladly trade a slight drop in pixel density for my Z2's much better color and contrast. The Z2 does have a strong vibration when typing fast, but not so much as to cause an audible rattle. When typing slowly or using swype it's perfect.
Also, battery life is almost as good as the G2, which as you know is really good.
Not that you care, but my phone history: Samsung SGH-N105, SGH-S105, Sony Ericsson T68i, Nokia 3650, 3220, Motorola SLVR L7, Blackberry Pearl 8100, original iPhone, 3G, 3GS, & 4, Samsung Galaxy SII Skyrocket, SIII, Note 2, HTC One, LG G2 & Pebble watch, Sony Xperia Z2 & LG G Watch (current)