Reputation ranks
Ranks only ever go up; points can drop but your rank stays.
About reputation ranksExactly what the title says. Every enemy is well-designed and engaging to fight, filling their own combat niches rather than just running at the player like vanilla mobs. The Terraria-esque system of locking spawns behind game progression is also a welcome addition compared to how many other mods throw their toughest enemies at you the moment you spawn into the world and gives the player new things to find as they get further into the game. The enemies also lend themselves to interesting new tools and weapons, making their drops actually useful.
The only real issue I have with Opposing Force is the odd addition of the tool and armor sets for vanilla materials. They feel out of place with the rest of the mod's content, and unlike its more original gear, aren't very useful or interesting. The wood armor set is at least a decent day one thing in the case of modpacks that make material progression harder, but I've never found myself wishing I could make emerald tools, let alone from lapis lazuli.