I prefer so called "Hard SciFi" which tries to pay attention to the known laws of physics when possible, so my favorite books usually have this in common.

Good Books:

• Metro 2033 - So descriptive, such a great world. It's a slow burn ghost story in a rich clostrophobic world.
• The Takeshi Kovacs Trilogy
  • Altered Carbon - The first and best book in the series, it's a masterpeice
  • Broken Angels - The second book, not as good as the first, but still some cool ideas
• Rendezvous with Rama - One of my favorites, great feeling of exploration and some really solid ideas in it
• The Three Body Problem Trilogy - This series, especailly book 2 and 3, are jam packed with some of the wildest, most well thought out SciFi ideas I've ever come across. It's just mind blowing.
  • The Three-Body Problem
  • The Dark Forest
  • Death's End
• The Bobiverse Trilogy - Really these three books are one long book broken up, but they constitute some of the best SciFi I've read
  • We Are Legion (We Are Bob)
  • For We Are Many
  • All These Worlds
• The Martian
• Artemis
• Snow Crash - It's a classic, and it has some good ideas. But boy does the writing style bore me at times.
• Ender's Game
• 1984
• Starship Troopers
• Neuromancer - Known as the grand daddy of Cyberpunk, and deservidly so. I don't know how it took me so long to get to this one.
• The Long Way to a Small, Angry Planet - This book was a wounderful suprise. The author is the rare bread that can write well thought out SciFi, AND good characters. It felt like reading a FireFly book.
• The Forever War - Great hard sci-fi, but a bit of a downer.

Bad Books that I love anyway:

• The Lost Fleet - This series is 11 books long. And the writing is not, how you say... good. But if you're really hard up for military SciFi, it's quite a good depiction of hard-scifi space battles.
• Old Man's War
• Decision at Thunder Rift