Ok, I really only have (off the top of my head) a few suggestions, and the first two deal with some other comments from earlier in the thread
1. Juggles: I agree that nobody wants to see Calibur turn into Tekken, but citing that SC2 mostly only had 2 or 3 hit combos gives the idea that that's what we wanna see. there should be 6 to 10 hit combos, provided their damage is reasonable and it doesn't take an extraordinarily long time to finish
2. Execution: Again, I half agree. There should be some moves or combos that require difficult execution for almost every character, however, for the love of god do NOT take it to the extent that other fighting games do. Do not turn it into a game *ahem, street fighter* where if you can't do one frame links, you can't compete at a tournament level. The difference between a combo where you miss the just frame and a combo where you hit the just frame should just be a little (10-20%) extra damage, or a situational ringout.
3. Soul Gauge/Soul Crushing: I loved the concept, but I thought it was a squandered oppurtunity. I think SG damage should be used as a balancing tool. No matter how hard you try, when you're designing a fighter, inevitably some characters are just going to turn out better than some others. You'll end up with characters who are less safe, or who do less damage, or who have worse ringout games. Balance that out as best you can first, then playtest it, and then, for the characters who end up doing a little more poorly than others, compensate them with a stronger soul gauge game.
There is no reason that a character like Voldo (who is, by the way, the coolest character in the history of fighting games, just sayin'), who has incredible tools, high damage, great mixups and a good RO game, a character who is universally considered top tier, should also have one of the very best soul gauge games in SC4.
Oh, and I'll tack on another suggestion
How about guard breaks that, you know....give advantage on block. Arbitrary lightning serves no purpose, and guard break moves that leave you at negative frames are just silly