My opinion after a few connection (Jazz) flights through the new T1
Clean, bright, white, sterile, boring...
Logistics are not good - WAY too much walking from check-in point to the gates, especially for regional connections.
Jazz (regional connection) waiting lounge (shared by several gates 105-112) is incredibly small and crowded considering the huge size of the building. There was standing room only, and looks like there is insufficient space to add more seats to the lounge, This was a big disappointment. A giant step backward from the individual waiting lounges for each Jazz gate which were provided at T2
gate 80 extension and later old-T1 gates AA
etc. Hopefully this is only a temporary situation.
Domestic gate lounges are on par with just about any other airport for seating capacity and space allocated.
Waiting times for baggage (domestic flights) seemed to be shorter than at terminal 2, but still longer than YWG
Also, some of the signage is ridiculous and will be very confusing to first-time visitors to this new terminal.
Overall, a nice, spacious building, and I'm sure some of the initial faults will be worked out as gate locations are finalized, walkways added and signs improved, but I don't find the cold, sterile decor to be a nice 'welcome' to YYZ