2 Suggestions
 

As the title suggests, i have 2 suggestions.
1.
Make abilities/types of armor class-specific. I am a thief, but i can cast like a mage... wtf?
Make there be class trainers that teach these abilities for a fee.

2.
Making land cannons more useful
As far as i know, land cannons dont have much of a use. Basically, you take potshots at enemies and ships... whoopdeedoo. waste of cannonballs IMO.
What i suggest is for cannonballs to have a blast radius, with knockback, and an ability to tell the general area where your cannonball will land. not a direct spot mind you, but it will give you an idea of where it will land. Much more efficient in my opinion.


I dunno, just some ideas :P