Yes, Deathstroke will be a great villain to Batman. He already is. In fact, he is sort of like the opposite of Batman in that they both don't have super powers and rely on their training and gadgets to fight. He is a great villain and challenges Batman at all times.
Deathstroke can be ranked as one of Batman's most formidable villains. Among most of the super hero's foes, Deathstroke is one of the most sinister and challenging for Batman to face. While classic villains like the Joker and Two Face are his most "personal" villains, challenging Batman more on a mental and personal level, Deathstroke is one to be reckoned with.
I like it, finally more villains in Batman movies, as much as I loved Joker in Suicide Squad we need more villains for Batman, he has so many villains. Its nice to see they will use them, we don't need Joker only. i would go with anyone but Joker, Jared was awesome but save him for now or use him as biggest villain which will culminate in Ben's last solo Batman movie or something like that, we really need more villains on big screen.
There have been a lot of great villains in the Batman series, and I look forward to Deathstroke as a great addition. One of the best things about Batman has been the evolution of villains over time, each with different powers and evil minds to be Batman's foe. Deathstroke is just the next in a great line.