This is some good stuff. This reminds me of flashback and Castlevania:Symphony of the Night in a weird way. I can see there's work and thought put into this so I apreciate it (on the purple mage guy's anim the way the text fades out is pretty interesting...though if you're supposed to actually read "atk+5" you should hold that for a little longer). The main problem is you work under the assumption smooth=good.
Each action has a rythm of it's own so there isnt a single feature (like smoothness) you can just add to every single one of your animations to make them look good. Each action has a subtleties and rythms of their own depending on the phisics at work, and the personality itself of the character.To make an animation of any action look truly impressive you must learn very intimately the subtleties of it's movement.
THIS is that stiffness you feel about your animation, when you make everything so smooth you're just standarizing every action and taking all the rythm and contrast out of the movement, making everything look as if the guy is getting an hernia trying to move under a waterpool.
I'm of the type of thinking that you should just look at the motions you want to create very closely and make an abstraction about what type of rythm belongs for that motion and then try and put that in your animation (try to do analyze real life actions, if you look at someone else's animation you're most likely watering down what they do instead of doing your own thing) look at a fireplace, and watch the fire...the fire is NOT smooth, nor is a bolt of lightning...same for human actions, every little thing has a timing of it's own.
I think if you should study the movmement on your own because if you have to be told how to animate everything you probably shouldnt be animating at all.However, of course learning from absolutley nothing is absurd. So I think I'll link you to some of the better posts of JohnK's blog
http://johnkstuff.blogspot.com/search/label/Cartoon%20College the guy isnt some kind of god spouting out a decree you should follow blindly, but he says some very true things and he's in general a very good guide.
PM me if you need some help with something in particular....try to tell me what you're trying to do with it what the character is like and what the motion should feel like and so on and so forth.