I'm pretty sure the 30 hour mark is easy to hit with most online multiplayer games (Shadowverse, Smite, Tera, etc.) but if we're talking strictly single player games...

Steam says I have 33 hours put into The Letter, and I haven't even finished all the routes or gotten all the achievements. It's a horror visual novel, but as someone who usually doesn't like horror you don't have to worry about it being overly scary. Shining Song Starnova is clocked in at 34 hours; it's a mostly linear idol Visual novel that I found surprisingly enjoyable despite not liking the idol genre much either. Both have free demos on steam if you to see if they're your cup of tea.

There are plenty of console or handheld games that would fit this too. I'm pretty sure most of the Pokemon, Final Fantasy, and Tales of games I've played have provided more than 30 hours of entertainment. My recommendations for each would be Emerald, FFX, and Abyss respectively.

I can vouch that my brother has devoted far more than 30 hours of his life to Shadow of the Colossus, Magic the Gathering, and Super Smash Bros Melee. My sister has spent over 30 hours on League of Legends, and I've also spent more than 30 on Yugioh. We all have pretty different tastes, so hopefully at least one thing listed appeals to somebody.