The Grandaddy of Halo: Part 2 (Better than part 1)
In 1994, Bungie released Marathon, an ambitious FPS for the Mac that was better than Doom in almost every way. It had a compelling plot with many twists and turns, alien slavers, an AI with questionable sanity, ingenious puzzles, and awesome weapons. You won't see a Flamethrower in Doom, but you do in Marathon! In 1995, Bungie released the sequel: Marathon 2: Durandal. It is now 17 years after you saved the Marathon and Durandal, the AI with questionable sanity, has just awakened you from cryogenic sleep. It turns out that after you saved the Marathon, Durandal stole you away from the ship and put you on his captured Pfhor ship.
Marathon 2 improves on its predecessor in almost every way. The graphics are much better for a start. The first one was all indoor, but this one has many outdoor levels. The lighting is better too. The guns also look better. There are also new weapons, such as a shotgun. The aliens also look better. The hunter is now starting to look a bit more like the hunters in Halo. Also, the troopers don't look as stupid as they did. All the graphics just look sharper.
The AI, of course, is very much improved. No longer are BOBs complete retards who will get in your way. Now, they are armed and they help you. The aliens are smarter too. There are also new kinds of aliens for you to fight.
The sound, sadly, isn't improved too much. The sound effects are great, but there isn't much music. However, the game overall is much improved and if you liked the first one or you like Halo, give it a try (it was released for free by Bungie, find it at trilogyrelease.bungie.org) Note: Gets repetitive after awhile. In fact, it gets so repetitive that you will never want to hear the game mentioned again. Good while it lasts, though.