In Career mode, you create a player, and help him make his way through the minors all the way up to the pros. You can create him for any position. When your player is in a game, he has goals that he needs to complete to further advance his skills.
You can also interact with the team by calling team meetings, or asking for more playing time. You can even choose to retire if you don't like the way your player is doing in the game.
If you like baseball games and also creating your own guy, then this game is for you. If you want a game that is tons of fun and really cool, then you will love this game.