Merrien finished in 30th place in a time of two hours, 17 minutes as fellow Brit Scott Overall languished in 61st with two hours, 22 minutes and 37 seconds.
And 33-year-old Merrien, who initially missed out on Olympic selection, said he is happy with his performance despite finishing more than three minutes outside the personal best he set at the London Marathon.
"I am pleased but I had a target of top 20. Given the strength and depth of the field, I felt that was achievable," said the Guernsey-born runner, who was also full of praise for the support of the home crowd.
"I didn't quite achieve that, but it was a strong field. I feel I justified my selection.
"The British public were absolutely phenomenal. I heard everyone talk about it (the atmosphere) this week. I knew it was going to be good, but it was better than anticipated. My ears were ringing.
"No British athlete will experience anything like this again."
But teammate Overall was less pleased with his performance as he admitted he was caught by surprise by the conditions of the race.
"I probably didn't plan for the conditions out there today. I really suffered on the last lap," said the 29-year-old Londoner.
"It was tough to hold back because the crowds were so big and they were shouting and cheering for the British guys.
"I should have gone out slower at the start. It is just one of those things."
Uganda's Stephen Kiprotich was the surprise winner of the Olympic title after defeating the heavily-tipped Kenyans Abel Kirui and Wilson Kipsang challenge to grab the gold medal.