Wrex's role in ME3 was absolutely confusing for me given what I knew of him so far. When you first meet him in the first game, he gets in trouble with C-Sec and then kills Fist, who was unarmed. If you talk to him later on the Normandy he'll tell you how he wanted to kill a good friend for money. The job he did for Saren was a piracy job. ("Checking bodies for valuables").
Bring him with you on Noveria, and he'll tell you how he had freelancer jobs here eliminating businessmen. Later he'll demand you to find him something to kill to get his blood pumping. Finally he'll make a strong case for killing the Rachni Queen using the same arguments that others use to justify the genophage. So in conclusion he was a pirate, a contract killer and overall a rotten and ruthless bastard (and I don't even mean it that negative or try to bash him, it's what made him interesting). He was also a prime example for me why people considered Krogans as dangerous.
Now in the third game all of a sudden I am supposed to believe that Wrex is some kind of wise and peaceful leader. He makes himself look like a pacifist, Eve tells you how he's the great hope for Krogans and no one seems even a bit worried about him. Even though he couldn't solve the situation on Sur'kesh peacefully. Padok Wiks had to step in to stop a gunfight. Even though he couldn't solve the situation with Wreav on Tuchanka peacefully. Eve had to step in. It was ridicoulous. In my 4 playthrougs I had Wrex one time, shook my head so many times in disbelief, and after that made sure I had Wreav in charge.
With Wreav the Tuchanka arc is actually quite satisfying for me. With Wrex it's messed up. If I at least could let my Shepard express some of the doubts that I had about Wrex it would be ok, but when I finally sabotaged (I also only cured with Wreav) and my Shepard got confronted by Wrex, the game makes her say "The other Krogans aren't like you Wrex".