I am fond of the good old action menu but it needs to be both more intuitive and faster to use. If I remember correctly this is something BIS said they were interested in looking at. So here is my suggestion:
1: Make actions avalible to the player always visible by small icons at the left side of the screen (this can be turned off in options).
2: Instead of rolling the mousewheel and clicking; just make the icons expand to an action menu when the player is holding the middle mouse button. By dragging the mouse during this hold the player can select an action and release hold to preform the action. This is much quicker and simpler than the current method.
3: The icons are important so that the action menu is as clean and easy to read as possible. When you have several weapons in your inventory you should easily see what action will select your gun and what action will select your AT launcher.