Halo: Combat Evolved: They gave it the name of 'Combat Evolved' for a reason.... It's shield system made every encounter with an enemy interesting and different, along with it's melee system, offhand grenade throwing system, and it's interesting weapons. Sticky grenades where a real ground breaker if you ask me. Another good thing about halo's combat is how different every weapon realy is, it also makes encounters more interesting. It's campaign was amazing, one of the first gameswith a very good narative, with people actualy speaking loads throughout the game, not known from in halo's era. It's story telling was amazing too. As well as inventing 'set piece' levels in the gameing world (e.g, the sniping mission). And just look at the art... The AI was groundbreaking at the time, with the good characters to back that up. The level designs where so massive in the campaign, which held epic battle after epic battle, never seen before in video games. This all backed up by the amazing soundtrack, which gives me the shivers just listening to:

"Brothers in arms"

http://www.youtube.com/watch?v=wbkQ99OxQJU&feature=related

"Under the Cover of night"

http://www.youtube.com/watch?v=BSqm5Id6Hw0&feature=related

"Halo"

http://www.youtube.com/watch?v=e6JK3fhYE1w&feature=related

It was an amazing game. You can't deny it, unless you are a total fanboy of some sort, and can't identify a masterpiece when you see it. This counts towards the new halo's too. Some people think the first was the best: This isn't true. The only thing Halo 3 was missing was BIGGER open battles then it already had (though they are still big). Also put into consideration the sequels are basicly the same kind of game, just with a new story and changed gameplay.