Halo 2 has so many great moments and play value, you'll find that this game never gets old.
So Halo 2... you Master Chief... and you get to kill aliens through a story driven FPS. Again. But there is a catch.
Let's start with the campaign. Co-op or solo, Halo 2 has the thrills to be up there with the best of them. The levels are decently diverse, yet you may see some of the areas getting bland. But it never loses it's great detailed combat zones. The thing Bungie did this time around was have the player control the Arbiter through a little less than half of the levels. Its makes for great gameplay using diffrent weapons, and ends up being an amazing way to tell a story. This is where I'll stop so I don't ruin anything incase you have never played the game.
The Guns in Halo 2 are the best I've seen in any Arsenal. Well balanced, theres' a gun for every situation. Weather your sniping from the corner of the map, or sneaking up on someone who is with a sword, Halo nails it. Every gun has a use, multiplayer and campaign, and you will come to be fond of every bullet-spitting weapon throughout the long tedious journey to stop humanity from becoming extinct and to shield earth from the Covanant raid.
Multiplayer is where this game is at. Lan parties. Xbox Live. Co-op. Anyway your running it, you will be cringing coming close to dying and laughing when you do.
So do yourself a favor and buy one of the greatest First Person Shooters to ever hit consoles. You'll be glad you do.