It doesn't look lie the adhesive was applied evenly. Not acceptable IMHO. Catch it before he grouts it.

He's grouted it. He thought it looked great. I haven't paid him yet, but I have 800 bucks worth of tile up there.

I'm sorry this happened. Lipping is a problem with this size tile (12x24) but my understanding is that it can be prevented by not doing the 50/50 brick pattern (I think it's a 1/3 pattern that's recommended). In the photo yours looks like 50/50. That being said it still seems like a bad job - I have 12x24 tiles in the 50/50 pattern in 2 baths and it looks smooth.

Funny you should mention this. I'm just having my backsplash done and was asking questions about tile in general.

My guy said the larger the tile, the more difficult it is to get it to look right as if the floor is a little uneven, you will get "bowing" - with smaller tiles it's easier to not to get bowing. Which makes sense, if you have an unevenness it will be like a "see saw" effect which is what you seem to have.

Is you guy an "experienced" tile layer? Maybe you should get another tiler in for a 2nd opinion
before paying the first contractor.

Most of these 12x24 tiles have a warning on them from the tile store not to lay them in a brick pattern like this. They are meant to be laid end to end only so these lips don't occur. It's really bad when on floors as they become a tripping hazard. Nothing can be done now but to remove them and start over I think. Or live with it.

I like the comment to get another tiler in. This contractor installed cupboards for me which was about equal to the value of the tile cost. Nothing pd yet.
If redoing it at his cost is not something he wants to entertain - I'm thinking he buys the tiles, too - I'll suggest he walk away and I have no charges.

Appreciate the suggestions re 1/3 pattern, but even in smaller areas the job doesn't look too good:

Thank you for bring this to our attention. I would never think this could happen unless someone told me. I had considered large tile around tub area. I can see where more than style preference has to be considered.

The man that is doing my backsplash is a tiler - he doesn't do anything else. If your installer is a "jack of all trades" pardon the expression, maybe he's not experienced enough in tiling to have done this job properly.
I would not be paying him for unsatisfactory workmanship.

We have these same size tiles in 2 of our bathrooms and they are fine, as long as they aren't in a brick pattern. They lay very flat. We did them in a vertical pattern and they look great.

http://floorelf.com/how-to-install-absolutely-flat-floor-tile

Here's an article about installing flat floor tile, which I'm assuming would apply to wall tile.
From what I'm reading it's not the tile, it's the installer.

He asked me how I wanted it laid...gave me the choice brick style or thirds i believe. I did say brick but wasn't aware this would be the result...