Game Design: Wii shoot 'em up

I enjoy playing most shoot 'em up games, so I thought, "If I could make one, what would it be like?"  When I thought of making it on the Wii, I knew what I wanted one of the main features to be (something that I would be surprised if it hasn't been thought of, although I don't know any shmup games that use it): aiming with the Wii remote.

You would move with the nunchuck and aim with the wii remote, and you could fire in any direction across the screen (your shot travels in a straight line from your ship to where you are aiming on the screen, and goes until it goes off the screen).  As a designer, you could do a lot more with moving the screen in different directions rather than just vertical or just horizontal scrolling, and you could also have enemies appear from any direction.  It would be an interesting new challenge, having to aim and move separately.  That would be like the main new concept of the game, but beyond that, there are lots of other features that I would consider including.

A big addition that I think would be worthwhile would be to have a secondary shot that fires in a set direction, this shot being more like one in a standard shmup game.  My idea for this is that the main shot would be controlled with A, and the secondary shot with B (or maybe vice-versa).  The secondary shot would be able to shoot in one of four directions (straight up or down, or right or left), adjusted using the arrows on the remote.  This feature would add in the ability to shoot in multiple directions simultaneously (and, as a designer I would make it necessary for the player to do this, in the higher levels at least), or to shoot at a single target with double shots.  I can already see a boss battle where you want to concentrate both shots at a boss, say, directly above you, but occasionally you'll have to switch one of the shots to hit enemies coming from below you.  And then more gimmicky/puzzle challenges: having to shoot a certain spot to negate a boss's defense and then simultaneously shoot the boss to damage them, or maybe shooting a switch to hold a door open while shooting through the door with the other shot.  Some variations are to include 8 directions for the secondary shot (the diagonals), or to have the secondary shot rotate and shoot in directions that are not perfectly vertical or horizontal while changing directions.  I probably wouldn't do diagonals, and I think I'd prefer that the secondary shot changes instantaneously rather than rotating.

I also love all the extra weapons and stuff.  I would consider having different weapons for both shots, and you cycle through types of shots with the buttons on the nunchuck.  There would either be a meter that refilled with time for each shot or items that give you ammo of a certain type of shot, and then the various types could be fairly evenly balanced each with advantages in specific situations, or else some would be really strong but quick to deplete.  The different weapons could be too much though, so maybe just one of the shots would have different types, or maybe no switching of weapons at all, but weapons get upgraded when you get items.  Of course, there would have to be bombs, maybe activated by 1, 2, or a shake of the nunchuck.

What else?  A button to speed up your movement or slow it down, or one for both?  A reason to not shoot constantly (save ammo or not hit things that shouldn't be hit), or else an option to automatically fire constantly?

One thing I dislike is how the games become repetitive and more about memorization than reactions.  I would try and do something to prevent every level from being identical every time, if not by creating various level configurations, then at least rotating the entire level or the position of enemies, or flipping the level horizontally/vertically at random.

Finally, more broad details.  Full story, loose story, no story at all?  I would ensure that there is some type of scoring or grading, although I'm not sure yet as to what I would give points for.  But yeah, this would be a game that I would love to try out.