I've just played the first three missions and, first of all, I do think the models in the cutscenes look off. But I keep reading people saying the missions themselves are bad and I'm left baffled because my experience has been quite positive.

The worker build times are spead up. You get to build far more units and upgrades than you usually would in a classic 'unlock one unit per mission and upgrades after' type of layout, a system which often leaves me a bit bored as an experienced RTS player. The story is interesting enough for the first 30 minutes of play in an entirely new IP.

Are they the most engaging missions ever released? Absolutely not, there introduction and tutorial missions where you learn the layout of the game, exactly like every opening to any campaign ever. I have no idea what people want from this first campaign experience that it isn't delivering. If you started StarCraft 2 and played the first few missions and found them significantly more engaging, I have new for you: it was due to a combination of you being younger and excitement from having played the first one rather than any difference in quality because these SG missions feel exactly the fucking same. Build marines and workers and run around the map and get introduced to the story, and this is accomplished just fine.