Some argue that it shows how "good" of a gamer you are.  The bigger your score, the better you are.  This can be misleading of course.  In the early days of Xbox achievements, Avatar: The Last Airbender - The Burning Earth was notorious for just this reason.  The game had only 5 achievements, all of which could be earned in less than 1 minute of starting the game.  There are many games that fall into this category and even more websites that will tell you how to get all the achievements for a game as quickly and easily as possible.  Having a lot of achievements may earn you some bragging rights, but it's hardly a quality indicator.

I like a good sequel as much as anyone and there are definitely games I look forward to that fall into that category.  As a somewhat embarassing example, I went to the midnight launch of Halo 3 and I couldn't wait to get home and play it.  But as soon as I turned my Xbox 360 on, I got the dreaded red ring of death.  You could hear my scream from the moon.  I turned it off and back on again in the hopes of some gaming miracle, but no dice.  My desire to play left me with only one option: go back to the Gamestop and buy another Xbox.  So I did, with the intention of getting my broken one fixed and selling it.  I did get it fixed but I never sold it which was handy when my second Xbox died later.  My point is even though it was the third game in the series and a lot of it hadn't really changed (the mechanics of Halo have been more or less the same through the whole series), I was excited just to have more of a thing I loved.  And it was a great game so my excitement was well founded.  It's easy to say that companies only make sequels so they can make more money, which does have a degree of truth in it, but I like to think that at least sometimes they do it for our sake more than theirs.

Perhaps the biggest question here is "Do games need a story?"  Certainly, there are many games that do not have a story, as is the case in many purely multiplayer games.  And there are even more games in which the story is just a setting/excuse for the player to go from one scenario to another and the plot hardly matters at all.  These games can be fun, but do they need a story at all?

Next talking point: Story in games

This is going to be a short one.  I love co-op as much as the next person, but after a while playing the same thing over and over can get old.  Games like Halo and Gears of War are a lot of fun, but the co-op in those games mostly consists of taking the main character and copying them multiple times.  Other games like Borderlands mix it up a bit by adding different classes, but many times the fundamental gameplay is the same.  Co-op can be more than just adding in another player who's a copy of the first one.