5 in particular, though, is changing the core mechanics more than any prior calibur game.
They added meter, that builds when you attack/take damage (every fighter seems to have meter now). Meter can be used to do EX moves (enhanced versions of regular moves), and it can also be used to do a Critical Edge, which is like a super/ultra from SF4. Each characters has a different purpose, some are more for combos, others for punishes or positional advantage.
Guard impacting will also use meter, but will be more effective than guard impacting in previous games
To replace guard impacting, there's now a mechanic called Just Guard. If you press block at the frame a move would hit you, you automatically perform a justguard which cancels a lot of the frames of block recovery that the move you blocked would normally force on you.
They kept the soul gauge/block gauge from 4, which I'm glad, because I really liked that mechanic, but instead of being able to perform an automatic round ender (Critical Finish) like in 4, it just provides a large hit stun state where you can hit anything you want, including a Critical Edge. (oh, if you aren't familiar, the soul/block gauge is a gauge that is hurt everytime you block, though it refills when yo'ure attacking. It's to prevent the overly turtling defensive style that plagued 2 and 3.
They're also adding a new kind of stepping called quick stepping that you get by double tapping up or down to step.
So there's a lot of core mechanics changes coming in 5.