Hot Scientist: Calleigh is a blonde, leggy Southern girl who likes guns, Natalia is Latina, Eric is half-Cuban/half-Russian and Maxine Valera is fairly cute. Also, yes, some people do find David Caruso sexy.
Jumping Off the Slippery Slope/Start of Darkness/Darker and Edgier: Seems to be going this way after his near-death experience. He is noticeably more vicious and ruthless, savagely beating a suspect and even letting a man fall to his death as he begged for Horatio to help him. Granted, one man had killed a police officer and was involved in a kidnapping, and the other man was a pedophile with a long history of abducting and molesting young female beauty pageant contestants, but still.
Pedophile: *While hanging onto a ledge* I can change - I know it! Horatio: I doubt that. Pedophile: *His fingers starting to slip* You have to help me! Horatio: *Coldly and dispassionately, while stepping away from the man* Do I? Pedophile: *Falls to his death*
The pedo's case was a bit more galling because he revealed/implied that he was also a victim of sex abuse before Horatio appeared - his favorite hiding place was where his "special friend" took him when he was a child.
There's another episode which ends with Horatio confronting a man whose job was supposed to be protecting pedophile victims who turns out to be a pedophile himself. Horatio tells him he's resisting arrest, to which he fearfully replies that he isn't (and he wasn't; he was just standing there). Horatio responds "We'll see how long that lasts." as he removes his sunglasses and wristwatch. He then steps towards the suspect as the scene Smashes To Black to the credits.
And yet Horatio allows the murderer of his wife, who's also Delko's sister to live.
He did go after him in Brazil. And killed him not only for Marisol's murder, but for killing his brother and trying to corrupt his nephew.
Tempting Fate: When walking into a jewelry store with Horatio, Speed discusses expensive cars, disdaining them in favor of his bike. Caine mentions that he might need "something with doors" some day. Speed says he has plenty of time. He is fatally shot not five minutes later.