Arsene Wenger and Alex McLeish have hinted Thierry Henry and Robbie Keane will be used primarily as impact players after temporarily linking up with Arsenal and Aston Villa respectively from Major League Soccer.
But Donovan has immediately been slotted into the Toffees starting line-up and Moyes pinpointed him as the man of the match in the 1-1 draw at Villa Park.
Moyes said: "Robbie Keane and Thierry Henry have come back to the Premier League from America and they need a bit of time to settle because of having a break since the end of the MLS.
"But Landon has come in and played three or four 90 minute games already on the bounce since he arrived and that says a lot. It's a testament to the professional he is. He was the best player on the pitch at Villa.
"His work rate was terrific. I played him on the right, left, then down the middle because he was the one who looked as if he had the energy. We've never had the chance to take him off in games because we need him so much with his running and the quality he has on the ball.
"Now we are going to try and give him a couple of days off so I don't burn him out before he goes back to LA.''
Donovan believes he is not yet at his best but is confident Everton can become a force once they overcome a lengthy injury list.
He said: "With my form, I'm getting there. I don't think I've been at my absolute best yet and I think I have more to offer Not a whole lot has changed in the two years since I was here. Of course, every time you lose players like Arteta and Pienaar, there is going to be a difference in quality.
"But the mentality is good and I think we are just a little bit away from being special again. Everton always seem to do well in the second half but you don't want to count on doing that. It's a little dangerous.
"But if we can get the four or five injured guys back then the manager will have decisions to make and it will strengthen the squad a lot.''