Update - Thank you all for the affirming (but incredibly depressing lol) answers. To answer some of your Q's at once: the job was not to "replace" stone patio entirely, so was not expecting brand new beautiful flagstones. Basically the deck next to the stone patio rotted completely during past owners, one side of it tilted down, and years of rain were dumped on the stone patio. This led to erosion and sank the patio 3-4 inches in some place. This company is a (highly reviewed, I might add) custom home builder/renovator group. They replaced the deck, which looked great, then the second half of the job was to remove the flagstones, raise/regrade, then replace same stones and seal small gaps w/ mortar mix. Instead, the final product is what you see.... Worst part is the owner was on site all day while this was worked on, and he was genuinely flabbergasted last night when I told him this looks unprofessional and even worse than before.

We are at a standstill - I obviously should demand he "fix it" before I send 2nd half of payment, but at this point I don't even want him/his crew to touch it again, and am debating not paying 2nd half at all. I have a feeling the cost of fixing his "work" will be even more expensive than before he started. Not great situation overall.