The versatile player has been involved in several pre-season games against Highland League opposition before completing his protracted move from Argyle, where he secured his release after they cut his wages.
Arnason was quickly persuaded to join the Dons following a meeting with manager Craig Brown and quickly realised he had made a good move when training with his colleagues.
"They looked sharp, I was surprised how good the boys are," the 28-year-old said. "I'm not being detrimental to Scottish football but you know how the English speak about Scottish football. They are sharp and it looks very good."
Arnason added: "I came up here for a few days and I spoke to the manager. I knew the manager by reputation. After that little conversation I was sold."
Brown was delighted to secure the signing ahead of the Clydesdale Bank Premier League opener against St Johnstone.
"He is an outstanding player, an international player of substance and calibre," the former Scotland manager said.
"He was the best player at Plymouth for the last couple of seasons."
Brown has expressed "cautious optimism" about Aberdeen's season after signing several experienced players to supplement the improvement he drew from the players after taking over in December last year.
Aberdeen also have Darren Mackie, Fraser Fyvie and Yoann Folly available after long-term injury but Brown knows there have been false dawns at Pittodrie before.
Brown said: "I'm criticised for using the phrase 'cautious optimism'.
"But I used that approach when I was manager of Scotland. I had 70 internationals and in 50 of them we weren't beaten.
"Even when we played the Faroe Islands and Liechtenstein I never said we would win those games.
"That's the approach we have in Scotland, you don't go boasting about what you're going to do.
"Aberdeen won their first two games last season and then had a very poor season so we have got to be cautious about everything."
The 71-year-old added: "I admire (St Johnstone manager) Derek McInnes greatly.
"He said this week his target was to ensure St Johnstone do not finish bottom.
"I thought that was very clever. We all know his team is going to be challenging for the top six but he has shown a lot of sense. I would like to do that with Aberdeen."
Source: Team Talk
Source: Team Talk