I'm currently watching TNG for the first time (up to S4 currently), and while Bev Crusher was definitely missed in season 2, season 2 has a few iconic episodes like Data's trial and Riker's exchange program. I wouldn't say the show is bad before S3, it's just that it's still finding its footing.

Something I definitely noticed is that the first 2 seasons tend to spend more time "setting up" the story of each episode, while S3 onward is when they begin to do more "in media res" starts to episodes. Those slow starts feel very similar to the TOS episodes that I've seen, while the "hot start" makes it feel a lot more like a modern show.

It reminds me a bit of how both The Office and Parks and Rec have weak first seasons. In both cases, it's largely because the first seasons of those shows involved them trying to replicate the success of another show (the UK Office for The US Office and The US Office for P&R) rather than understanding what their show was going to be, particularly with the tonal differences and the strengths of the cast. A lot of the problems of the first season of TNG seem to be caused by it trying to be too much like TOS.