Despite featuring in Aston Villa's relegation to the Championship, Gueye gained admirers for his style of play in the West Midlands and Koeman has described the Senegalese international as a "great signing" after he helped the Toffees into second place in the Premier League table.
The 53-year-old told reporters: "The adaptation of the players hasn't taken long.
"He is playing comfortable. He puts a lot of energy on the pitch and he's comfortable on the ball. He's a great signing."
Gueye is expected to feature when Everton face Bournemouth on Saturday afternoon.