It's fortunately not far enough along to see many mistakes yet. I don't know if it's lens distortion in the bottom image or the wall actually curving, but that edge looks curved. Where the sheets come together in that bottom image, though, there's definitely a butt joint that's too tight. There should be at least a 1/8" gap for the joint mortar to fill. The big gaps in the butt joints that you seem to be highlighting elsewhere aren't a problem. A little too wide is stronger than a little too tight. Typically before tiling,
- the whole thing would have alkali resistant tape bedded in mortar at all of the cement board joints and
- the whole thing would have a waterproof membrane painted onto the inside surface (it's good practice to buy fiber reinforcement for the waterproof membrane at inside corners, especially the bottom corners, the curb, and up the side corners a couple feet). I suppose you could have a waterproof membrane beneath the cement backer board, but virtually all installers paint the membrane on the inner surface now.
These steps are messy, so a work-wise installer would complete that stuff before installing any tile. It looks like it's already too late to get the bottom joints taped and the floor waterproofed.
For a shower, the most critical details are in the floor, so I suspect that there are already blown details under your tile.
If you don't know much about tiling and whoever put down that tile doesn't either, then your project is going to end in disaster. If you're looking to learn the nuances so that you can coach somebody else through the process, then Sal DiBlasi owns my favorite tiling YouTube channel. If you're looking to hire somebody, then I suggest imposing the TCNA Handbook's quality standards on the job. If you're blissfully ignorant and your contractor candidate doesn't own a copy of the TCNA Handbook, then you shouldn't hire him. Maybe I would make an exception for somebody who does nothing but Schluter installs, where the surface quality of his prior work could indicate sufficient technical knowledge.