The viewfinder on the G1X is indeed below average, bordering on horrible. I have become quite reliant on the ability to frame and expose accurately using an LCD screen, so a small non-TTL optical viewfinder with less than 80% coverage is next to useless for me. I have seen some G1X users defend the optical viewfinder so it obviously has some value, but my view is that it either should have been replaced with an EVF or removed entirely.
The build quality is generally very good as per previous G-series models, although it is hard to make a plastic, articulated screen feel as solid as the last of the fixed-screen models (the G10). The deeply textured rubber grip is also a nice feature. The grip itself is quite discrete and only extends forwards from the body about 5mm, but the rubber texture makes the grip look and feel a lot more substantial than it actually is.
My impression of the sensor is that it is as good or better than any Canon APS-C sensor that has gone before it (as you would expect), and the closest EF/EF-S lens that I can equate the G1X's lens to is the EF 24-105mm f4L IS USM (optically, if not in build quality).