Wally West, probably the only Flash I actually like is one of the funniest and sweetest characters in the DC Universe. His personality is greatly reflected in the way the story in this episode is told.
Flash and Lex Luthor have switched bodies. This leads to alot of comedy with a powerless Flash trying to fit-in with the villains around him.
Clancy and Michael give some of their best performances here. Though Michael is pretty good as Lex in Flash's body, he lacks the same intellectualism that Clancy gives to Lex's every word. He's more disdainful than sarcastic. I think he tried to hard to sound like the Lex he plays on Smallville. That Lex is a very different one from the one on JLU, but I dunno.
Clancy on the other hand is a perfect flash, he has great comedic timing and delivers those perfect moments such as when he adresses a gathering of the Legion of Doom in third person. "Lex Luthor is pleased. Carry on."
I guess Michael didn't have as much to work with. Lex as Flash didn't have alot to work with, as he had very sparse dialogue.
I really liked Tala in this episode, and her unintentional crush on Wally. Poor girl is stuck with so many jerks for boyfriends, a nice guy like Wally must be a nice break.
The thing that really brought this episode full circle for me, however. Was the fact that instead of switching voice actors, so Clancy was doing Lex in Flash's body, and Michael doing Wally in Luthor's (With the villains dismissing it as "What happened to your voice, Lex."-type lines). They kept the voice actors to the bodies. Real nice touch, as I outlined before.
Great episode, really deserves that 10 out of 10.