FWIW, I would have all of the same concerns as you.

On the floor... Unless you do individual tiles (which is what I would do) then I don't think it's possible to completely eliminate the sheet lines but they can be much better than shown in your photo.

Is the shower head centered? The niches s/b equidistant on each side of it. Did he just stick them in based on where studs were instead of redoing the studs so that they'd be set properly?

niches--edging looks fine.

If you wanted a different approach, that should have been specified. It would include different tiles with available bullnoses, a shelf at the bottom or other methods.

Centering the niches on the showerhead may have required re-framing the shower, which may not have been in his contract.

The flooring would have worked better with a different choice of tiles, such as the pebble tiling below with less defined edges.

The floor tiles are poorly placed. The grout spacing between sheets should equal the grout spacing between the individual rocks on the mosaic. In your mosaic choice, there are variable grout lines, but the space between the sheets should not exceed the largest space between the rocks on the sheet, as yours does here.

It might be the fault of the framers about the niches, I am not experienced enough to know. But they do look wrong. Since tile edges are not attractive, something is required to make the edges of a niche look "finished." If you did not chose a tile that had a bullnose or a pencil edge available, then they had to use something. Kerdi (and I imagine other brands) sell this metal tile edging for more modern-looking tile installations. Yours looks fine to me, but the contractor should check with you about what you want to use for edging.

I'm planning my master bath remodel, and what you ended up with would be my nightmare. Which is why I am using the same Designer who did my kitchen. She explained that those pebble tiles are very labor intensive to hand set and not have the sheet lines. It was an extra 1K just for that choice, and I didn't like it well enough for that. I'll do he 2x2 that match the wall tile instead.

She also explained that a lot of tilers use pre formed niches, which don't line up with the tiles that I might pick. So she recommended that we do custom niches if I wanted them. That was also an expensive upgrade, so I decided a couple of corner shelves would work better.

This bath is turning out to be almost as expensive as the kitchen that I did. But I'm not second guessing any of it, thanks to my designer. I know it will be done right.

The grout spacing between sheets should equal the grout spacing between the individual rocks on the mosaic.

True.

The tiler did keep the line as tight as possible at the corners, but the placement of the stones on the tiles made it impossible to continue that spacing.

The edging on the niche looks like a Schluter edge. We have it in white in our new bathroom. I think the silver looks nice with your tile.

I paid over $5K just for tile labor for tiling a small bathroom (tile floor and tile surround around tub), so in my area you would not have paid enough to get a really good tile professional.

I would be very unhappy with entire job. I think a re-do is in order here.

Wig it is any cosolation I paid over 5 k to just have a shower waterproofed and tiled so your price is on the very low side in my area. How did they prep your shower?

New home under construction. Framing for the niches should be shown on the plan and built that way if possible long before the tile contractor starts. Many times structural posts and vent pipes etc. prevent stud bays from being easily moved later.

The shower floor sucks. I don't like the materials as it looks like it doesn't interlock naturally (as said above). I'm not sure there's an easy way to make it look good. Find out what your options are to make it look better.

Grout selections should be in writing on a list room by room with the tile selections, so the contractor can read it, copy it and work with something larger than a 2x3 screen. Not all those texts go through and the shear volume can be overwhelming. Email a signed PDF.

The Schluter styled metal is everywhere in practice today.