The best case scenario with the meeting is that Trump spent two hours ranting about Mueller, Clinton, and the American deep state to Putin, and that nothing was said about Iran, Syria, or Ukraine. The worst case is virtually anything else, because it is only too likely that Trump would give away the store in exchange for, well, nothing.
Putin isn’t going to change his position on Ukraine or Syria, Trump doesn’t know enough about nuclear weapons to engage in a serious discussion about arms control, and Russia has nothing else to offer us except, perhaps, a free hand with Iran. Substantively, the whole idea of the meeting was a waste of time; optically, it was a victory for Putin, and a disaster for everyone else.