My top five:
1. Spyro the Dragon (Spyro 1, 2, 3) - These games are really the most special, and most important to me as a gamer. In a similar manner to MLP: FiM, the first three Spyro games have a very charming feel to them. They have the most heart, humor that isn't too childish nor adult, a great visual style for the time, solid music, great & simple gameplay, and just overall FUN! So far, no game has replaced these game as my top. Now, I love the Spyro series as a whole, and that includes the Legend & Skylanders incarnations as well, but the originals stand out.
2. The Elder Scrolls V: Skyrim - What can I say that hasn't been said? A large world to explore, fight dragons, many unique dungeons to loot & explore, an awesome villain lore-wise, etc. I'm currently replaying this game, and it never fails to put me in utter awe.
3. The Witcher 2: Assassins of Kings - This game was a real treat for me. While it didn't have the world of of Skyrim to really get into, the story & characters are what really steals the show! While the gameplay takes some time to get used to and the difficulty can be testing, you will be hooked from beginning to end by these interesting & deep characters, and the amazing story. Really, it is the Game of Thrones of gaming!
4. Dragon Age: Origins - This game really intimidated me when I first got it a few years back. It just seemed to complicated! I tried it again last year with determination, and the 60+ hours I spent on it were damned worth it! With it Lords of the Rings feels to it, it feels SO big and the stakes seem big as well. It feels somewhat dated, but the gameplay works rather well! After getting used to it, I really just drug me into the world! Not to mention the character interactions were amazing as well!
5. Prince of Persia: The Sands of Time - While age hasn't been that kind to it, the look & feel of the game never fails to drag me into it's mystical hold. The Prince remands one of my favorite game characters of all time, and the world of Azad is still amazing fun to traverse. Of course, the acrobatic gameplay & the use of the Dagger of Time are what steals the show for me. Amazingly fun!
Honorable Mentions: Castlevania: Lords of Shadow, Shadow of the Colossus, Phantasy Star IV, Sonic the Hedgehog (1, 2, 3, Knuckles), TIE Fighter, Age of Empires, Uncharted (1, 2, 3, GA)