So, my idea is that alternate attack could add more gameplay. The alternate attack would be stronger than normal attacks and have a different animation, but still acts as an regular attack.
For exemple : I the player attacks some ennemy and he is almost dead. The player decides to use his alternate sword attack, and thrusts his sword in the opponent's chest (the area may depend from where you are pointing) killing him... or almost killing him... or getting blocked by the ennemy.
On the side, if he is attacking an ennemy with full health, the player's alternate attack success is greatly lowered.
Now, why i don't really want finishing moves (well, sneak attacks are ok), is because the animation takes some time, so the ennemies around us wont attack us if we finish one of them... there for, making the AI look unfinished...
For magic...the player could "[censored] slap" the ennemy while casting fire ball...
Nah, magic is different, and sadly may not have alternate attacks...
If you have some question, or if something isn't clear, comment on it.