His offensive skillset is very good. He has outstanding skating and puck control at speed, making him dangerous in transition and in the offensive zone with the puck.
What was unclear was whether he would progress in two areas: 1) determination and playing through physical encounters; 2) reading the game and vision. Those are the two areas that seem to have really improved over the past season and a bit. He is still slight and lacks physical strength, but he is not shy about playing in "hard" areas and absorbing hits to make plays. Also, he has improved in moving the puck quickly when that's the better play, and he's scanning the ice more when he has the puck, and finding teammates with passes after he's created space. Those are two keys to success at the NA pro level.
I would also say that his shot appears to have improved, at least in accuracy. He's starting to snipe goals around defenders, finding the edges / corners of the net.
With those developments, he's become a much more promising NHL prospect, who should now be firmly in the discussion for top-6 NHL potential.
One last point... the Jets are developing Lambert at C in the AHL. I'm not sure that's where he'll make it at the NHL level, but he doesn't look out of place there in the AHL, particularly showing good defense and transition in the D zone.