In that case, I'll throw out a couple of my favourites, with description, and you can watch what you like.
Stiens;gate: The story of a group of college freshmen who form a wierd science club in the protagonist's apartment. The protag is a self proclaimed mad scientist who accidentaly creates a time machine. The rest of the story focuses on experiments and consequences of the time machine
Higurashi No Naku Koro Ni: The story of Hinamizawa, a rural mountain town with an anual festival and a dark, murderous secret. The protagonist, Keiichi, has to solve the mystery of a demon god's curse withpout becoming the next victim. Also, it has several arcs, and after one ends, the story restarts from an earlier point. After the first one ends, the reason why should be fairly clear.
Paranoia Agent: There is an assailent on the loose. A young boy with a bent bat, coming after desparate people. Are you alone? Are you afraid? He could come for you any moment, you know. Just who is he, and where did he come from? No one knows. But he's coming for you.
Code Geass: In a word where america was never born, the holy brittanian empire rules. with their superweapons, the knightmare frame mechanized armor, they have taken over countless countries, including japan, which has been stripped of all honor and custom, and redubbed area eleven. But the elevens won't back down, and rebels rise. Our protagonist, Lelouch, rises to lead them for his own ends, using a mysterious power called Geass.