Warriors ran in five tries in a fine 42-13 victory in the European Champions Cup opener at Scotstoun.
Speaking to BBC Scotland. Gregor said: "It was a great result and a fantastic start to our campaign, to deny them a bonus point and score maximum points ourselves.
"But we could have been much better. I am frustrated with a few things.
"We didn't execute some of our set-piece plays very well.
"I thought our forward pack were outstanding and we put them under so much pressure, but we could have had a lot more reward for it.
"With the pressure we had in the scrum, I am disappointed we didn't come away with a try, and it took a bit of inspiration from our backs to get the momentum back in our favour.
"I am listening to myself being critical when it is such a great start but there are a few things to improve for next week.
"We gave away too many penalties in the first half. But when we managed to get the ball, our forwards were carrying really well, with [scrum-half] Henry Pyrgos putting them into the right areas.
"I thought both half-backs played really well.
"Finn [Russell] was outstanding, especially in the first half with some great kicking.
"He trained really well this week, is back full of confidence and both he and Henry realised where the space was.
"Some of Finn's passes, moving the ball wide when it was on, were excellent."
Finn Russell was the subject of a tip tackle by Matt Toomua, for which the Australia centre was shown a yellow card.
"It was a dangerous tackle," was the Glasgow head coach's assessment.
"By the law, because he didn't land on his head, it wasn't a red card, but the only reason he didn't land on his head was because Finn put his arm out.
"It could have been a red, but it didn't affect the outcome. Finn got straight up and that was great to see."