Halo 1 had a cool story but the inability to duel wield weapons makes me unable to play it any more. I go back when i want to play the story but i love the duel wielding feature on Halo 2.
As for the rifles, the 1 in Halo 1 is an assault rifle. Full auto with no scope. The one in Halo 2 is a battle rifle with the semi auto fire. Basically the Battle rifle is the evolution of the pistol in the first halo. The pistol was a beast in Halo 1 with a scope and extremely far distance to hit the enemy. The pistol in Halo 2 is just your ordinary Magnum.
Both games kick ass in my book. I could do without the sword for online play though. Too easy to kill people with and the noobs always lean on it.
Plus as far as the needler goes, i'd check your diffuculty setting. The needler was worthless in Halo 1 on anything above normal. You could shoot forever and a grunt wouldnt die with it. In Halo 2 it can do some good damage when coupled with a plasma rifle or pistol.
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