First, is that the wheels are large, and I would assume relatively low pressure, implying, as is consistent with Russian doctrine, that it is intended to operate from poorly prepared fields.

The second is that it has relatively small all moving vertical stabilizers, which implies to me that thrust vectoring might be a part of further development, though there was no evidence of such in the initial videos.

Also, the wheels were never retracted, but this is not a surprise on a first flight.

There is also what appears to be a not-particularly-lo IRST on the nose.

Also, if you look at the somewhat more detailed video, it appears that the leading edge of the leading edge extensions (a mouthful that). Aerodynamically, it appears to me to be rather similar to the leading edges of the inlets on an F-15, which pivot down for better pressure recovery at high angles of attack.

Also, lots of rivets on a closer look in the new video, which implies that this is, as I originally surmised, a demonstrator rather than a true prototype.