This is all for the good - continuity and change. O'Brien and Smith had a strained relationship and one had to go.
It is almost unanimous on this board that the Texans lack overall talent at starting positions and depth, particularly on offense. By contract, this is on the GM.
The organization has now delt with this by hiring Gaine. Only time will tell if he can do the job, but by all accounts, he will have a better working relationship with O'Brien.
Having elected to go with change at the GM position, the organization has elected to go with continuity at the coaching position. With Smith as GM, I'm not at all certain that O'Brien had the players that he would have liked to have, and never had the opportunity to fully show what kind of offense he could put on the field.
Now, with the QB position settled (assuming Watson can come back near his past performance, and this is still in doubt) O'Brien is in the driver's seat.
This off season will be interesting, to see how O'Brien and Gaine address our deficencies. I'm hoping they take an aggressive approach.