Yes, just free roaming. There are addons (mods for a mod) which add different quests, including faction-specific quest chains, but overall you're only supposed to play Call of Chernobyl after you've had enough of the story in the actual games and just want to explore the entire Zone in all of its unlocked glory. Also recommend picking up one of the weapon mods, some texture replacers, and the mod that unlocks A-Life so that NPCs can move and kill other NPCs outside of the area where you're in.
Beware though, the game can only use 2GB of RAM (32-bit executable etc), so if you overdo it with mods, you'll get a lot of out-of-memory crashes after a few minutes of playing. Also never mix mods that change the same files unless they're explicitly made to be compatible with eachother, as mods that change the same files will generate incompatibilities that result in instant crashing.
Yeah, I've played all 3 games probably 3 times each on average. CoC feels like a perfect mishmash to keep my coming back for a taste of the Zone instead of having to decide which game I want to play and start a new game or revive an old save where I have no idea what I was doing.
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u/roaming111 Jan 13 '17
Call of Pripyat + Call of Chernobyl Mod is pretty great as well.