I sat in a D seat on the 77G two days ago and was prepared for the absolute worst. I lucked out with an open E seat, but my biggest concern was the width of the foot space on the aisle side. Even with a size 12 shoe on, I was able to extend my foot comfortably in the space. There still is an awkward metal support between your feet, so it's a weird layout if you extend your feet straight out, but I was also able to sit with both feet crossed in the aisle-side space. It's not ideal, but it's not disastrous. Admittedly... it would be worse with a stranger in the E seat.

The outboard triples are clearly preferable, IMO, but I wouldn't hesitate to pick a D/G seat again if the other aisle/windows were taken, or if I was sure I wanted an aisle seat for a given flight.

We know the cons, but here are a few of the pros of the 77G after 5 Y flights:
- Lavs (better ratio than E70/E75/A319/320/73G/738, more spacious, better layout in cabin, fwd Y lavs have int'l J amenities)
- Larger bins
- Tablet holder in seat
- Translating seat pan recline mechanism (^)
- Better-positioned ISP outlets for non-bulkhead (mounted on row in front rather than behind your knees)
- More space to walk around, stretch, chat with other pax (at crossaisles)

That's about all I can think of for now. It's not a particularly comfortable configuration, certainly less so than the previous 77H or three-cabin 777s, but I still think it compares favorably to a 737. YMMV.