It doesn't seem to have an option to play a complete season on the DS, unfortunately. You can play a single exhibition game (Match Play) or you can go through the playoffs. I like it, though hitting seems tough to me.
I've noticed a second mistake in the first MLB Power Pros (my copy is the PS2). The first mistake I found is that they put the wrong Molina on the Giants' roster. Lately, whenever Chipper Jones or Adam LaRoche comes to the plate, the announcer refers to whichever one it is as one of three 30-HR hitters on my team. The problem is I only have two. After those two, the most HR I have is by Brian Giles who currently has about 9. I can't complain about that too much...especially after all the other announcer errors (like where he first says a ball is stroked for a hit except that it's a fly ball that gets caught)...