It looks like the tiler simply tried to carry the vertical grout lines on the shower wall down and through the niche's back wall.

I think it's fine. You either end up with the wall and niche grout patterns aligned and the narrow pieces inside the niche, OR you have different grout patterns on the niche and wall. One or the other.

If your grout color is similar to the tile color, the bold contrast of the ungrouted grout lines will recede a bit once the grout is installed.

I actually like the look of the captured shelf and the returns that cut into the shower wall. It looks like a one-piece seamless shelf? While the one-piece shelf install looks nifty, I have to say I do prefer a tad more effective pitch on the bottom shelf of a niche.

Thanks for weighing in, Mongo (really, what would we do without you?). The shelf is 2 pieces that meet in the inside corner. I'll ask my contractor about the pitch--early on he said they do a very *slight* pitch. I'm disappointed he didn't listen to me about creating a different pattern within the niche, (he did the same in the other bathroom)but I'll live with it. It's crunch time and I don't want to rock the boat too much.

for what it's worth i really like the marble base, i agree it is a classy touch

Thanks! Should the areas around the shelf that cut into the tile be caulked, since it's two different materials, or grouted?

I agree with Mongo's assessment (no surprise!)

What color grout are you using? That will have a big impact on how the finished niche looks. I think it's a pretty cool design to have it wrap around the corner. I don't recall seeing one like that before but I like it!

We have returns on our granite niche shelves... by our own design.

I'll be using Tec grout in Silverado. The niche wasn't in the original plan, so when I decided to add one I had to squeeze it into a corner because of the plumbing, and it didn't seem big enough so we continued it on to the other wall. Plus, I wanted something a little different, and decided against one large niche on the other wall. My inspiration was the niche in this photo (see link)

Here is a link that might be useful: Corner niche

Can we see the rest of your shower? I think with white grout it's totally fine. I was concerned about a few tiled areas (I think we used the same exact tile) until the white grout went in, then everything I was a little concerned about disappeared. I don't know that I would rock the boat here - I'm not sure how they could have done it better - they have the walls and the niche framing to consider, and the running bond pattern. Unless you were very very specific about how you wanted the tiling to happen in the niche, I wouldn't mess with it. Just my 2 cents.