Games

Because it's been like 20 years since I've played it I unfortunately can't recommend any mods by name so instead I'll tell you about this goofy mod I installed once: It added a pretty long quest in which the creator added their own fully-voiced NPCs—including children—so when you interacted with a kid you'd hear them talking in a voice that was very clearly a grown man trying to pitch his voice as high as possible. That memory has stuck with me all these years because it was so unexpected I burst out laughing the first time I heard it. I have to give them credit for going through the trouble to record all that dialogue though.

Also if this is your first playthrough be sure to do the Dark Brotherhood quests at some point; they are some of my favorite quests in the game. My only other suggestion would be to occasionally stop and watch NPCs interact with each other. Oblivion has a well-earned reputation for having some really funny NPC interactions.