Yeah that is not good work at all. Probably not an actual tiler that's done it? Should have really used a cement-based adhesive due to the tile size. Trim isn't very good. Gap around ceiling does seem to follow the ceiling and tiles run in suit (not jutting around higher or lower etc) but the gap is too big for the recommended industry standard of I think 6mm (don't quote me).
Who employed this 'tiler' did they check their references? That quickly gets rid of the blaggers.
If it was just a case of going with the cheapest quote, then this is what I'd expect from more than 50% of them.
First you have to give the person a chance to correct the issues. So list them. Get the adhesive checked by calling the manufacturer of the adhesive. They're good in the UK and will try help. But you need them to say it's wrong first, then the tile will need to strip them back and do it again properly.
At this point, he will probably go AWOL, but might stay with you and keep working with you. If so then it's a case of taking them to court to get the money back from you paying a real tiler (I can help you use the forum to find one if you wish). If you do end up using the courts, The Tile Association might be able to provide the required expert witness report, its not cheap but might be needed.
Hope this helps. I'm so sorry you've experienced this. That person isn't a tiler though. They'd have known first of all that the adhesive is not right.
Are the tiles porcelain or stone?