I’ll second Pandemic. Easy to learn and one of the best cooperative games I’ve played. Lots of expansions available to keep it interesting if you get hooked.
For a creepier, mystery type thing, check out Betrayal at House on the Hill. Cooperative house-exploring game with lots of problem solving type things… and one person ends up being the evil villain.
Another mystery type game that’s like that but way more complex is Mansions of Madness, where you and your friends are paranormal investigators trying to solve a mystery and explore a house. There’s ghosts and monsters and lots of horror and puzzle-solving. This game’s notorious for its sheer complexity and number of card decks, etc, but the new version uses a free app to “GM” the game, which is a huge help.
