In its place is a 'might' meter which fills as you land hits and other moves. Well, the combo meter is functionally gone in Shadow of War. This was indicated by your combo meter turning red and certain button prompts appearing. Once you got your combo high enough, you could use certain abilities. In Shadow of Mordor, abilities worked on a combo system.

Reaching the second act will also blow the Nemesis system wide open, unlocking new features like death threats and outposts. And speaking of basics: rush through the first act to unlock several awesome core abilities which I won't spoil here. Shadow strike unlocks some dubious stealth options and really speeds up traversal. I recommend knocking out some basics like executions and mid-air shots, and then focusing 'shadow strike,' which lets you teleport to and instantly kill enemies from absurd distances. Abilities work on a parent system, meaning you have to unlock them in order from left to right.