I personally wouldn't say he had a great game but I think I agree with others, in that we appreciate the work he does for the team and how it's important to see those contributions for what they are separately to other factors; like as ridiculous as it sounds, the fact yes he was at fault for two goals conceded.
I'd go into more tactical stuff but to put it simply if Carrick was playing instead of Morgan, we probably wouldn't have conceded those goals but imo would have lost the game 2-1/3-1 or something. Morgan's energy levels allows the team to be more expansive (by freeing your Herreras/Matas) and with that comes risk. The first goal absolutely was his fault, the second iirc he was defending deep (edge of box) and made a poor pass/clearance straight to an Arsenal player.
Granted it was a toothless Arsenal but they were in the ascendancy and were the better team with the ball with their fluidity; we were scared and bottled a lot of clearances but at the same time Morgan was crucial in being so disciplined.
Anyways the issue here though is people's opinions on player praise/criticism.
Here's something for thought, Martial is no doubt brilliant but bar 5-10 games (all season even), on an individual level he has actually been quite dreadful. Consistently poor end product, although great defensive work, poor attacking positioning and lack of any goal threat for someone, who gets free reign on the ball.
It's not an inaccurate criticism at all and yet, we would have many in the Martial thread disproving that. It's the same with Morgan's display against Arsenal. There's too many intangibles to consider to make simplistic criticisms.