I played for a few minutes and what you have is decent. You have a good basis for a DBZ game here, but a few things are missing and there are areas where you could improve.
1.) The first thing I noticed was the control layout. This isn't very "attractive" to most people. Most people prefer to use WASD to move and other keys are usually mapped to different actions, such as "B" to punch, "J" to transform, etc. I suggest having customizable controls, so that people can map keys to the actions to make playing more comfortable.
2.) I know this is just a demo, but presentation counts. You should work on making a good menu when you get the chance.
3.) You should probably add sprinting to the game to make getting around a lot easier. Its been a while since I played the original games, but I think those games had sprinting/running. Hold a button and just press/hold the movement keys.
4.) Add "Free-flying" - I know the original games did flying very loosely where you could only fly at certain points, which I always found to be a bit weird and limiting. What I would suggest is adding a free-flying system to where you can fly around while exploring the open world as normal. Free-flying would need to drain ki as your flying around and should move your character much faster than while sprinting or normal walking.
5.) Add ki charging & guarding - This is an obvious suggestion, I know.
6.) Add more depth to the melee combat - I'll be blunt with you, the melee combat isn't very fun and its lacking. The character I played as, Goku, has only one basic combo string. Its been a long time since I played the original series mind you, but I think even then those games had more going on when it came to melee (or perhaps my nostalgia for LOG2 is messing with my head). Anyway, I suggest you add another series of attacks to the current string. Maybe have Goku take a step (move forward a bit) and deliver a kick after the melee button is pressed (after the second punch). What would be cool is allowing the player to extend their moveset using "skill points" awarded when a character levels up. Maybe there could be another animation after the kick where Goku follows up with a chop or something.
Hope I'm explaining what I mean well. To recap and simplify what I mean:
[1] = Punch
[1] [1] = Second Punch
[1] [1] [1] = Kick (step forward a bit)
[1] [1] [1] [1] = Chop
Another suggestion I have is to add another melee attack button like in the current DBZ games for heavy attacks. These attacks could deal slightly more damage than a regular attack and possibly cause more knock-back [to the enemy], but could be slower to pull off. Having heavy attacks in the game would add more depth to the combat and allow players to really deal more damage up close.
My last idea for spicing up the combat would be to add chargeable melee attacks. Similar to how DragonBall Xenoverse does it where you can hold down an attack button and release it to temporarily stun an opponent or break their guard. This could be useful to temporarily slow down an enemy or two that are chasing you down.
7.) Adjust the a.i. - My last suggestion would be to adjust the enemies, so that they aren't ki spamming, so much (a problem I also have with the new DragonBall games). The ki spamming will be less of issue if you decide to implement my flying and sprinting suggestions because this would give players more options besides teleportation for getting out of the way.
8.) Improve animations - Some of the animations (like Gohan moving up or down) need work (moving left & right looks fine). Also, is me, or is Kamahamahae missing a few frames? You should be able to charge that move up like they do in the anime.