WARNING! LONG POST!
First off I must say that this game is by far the most fun and enjoyable fighting game of this or any decade. I won't say it's the most competitive, since I don't have a deep knowledge about this specific subject, but it's certainly not a broken game.
All those things in this game that differs it from any other fighting game (dial combos, crossover jumps, projectiles don't collide, block button, etc) is what keeps me playing it over any other game since April 19th, and I have no plans on quitting it!
BUT, no game is perfect, and even MK has it flaws. There are a few things in this game that I want SO BAD to be changed for MK10, since Ed Boon said they're sticking to this game's mechanics.
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1. THROW BUTTON TO TECH THROWS. Seriously, a specific button to tech a back throw and another for a forward one? This is plain stupid, and we all know this since day one. Using the same button(s) your opponent pressed to throw you is the most logic way to tech it. SF has a perfect example on how balanced this mechanic is, and this should be implemented in MK ASAP.
2. INSTANT 50/50 AFTER A BLOCKED ATTACK. As I said before, I really like the block button, since it prevents all those stupid footsies/chess-like boring matches. But the BLOCK ITSELF in this game is definitely HORRIBLE. Everytime we block an attack we're STUCK on that atrocious block animation, and it makes those moves that has a not-that-quick-recovery simply GODLIKE SAFE. And those moves which has a very quick recovery, such as Kung Lao's [1,1], allows you to MOVE and JUMP while your character is still with their arms raised like "Hey look at me, I'm trying to block the wind! I'M F*CKING RETARDED!". Seriously, WTF? This garbage NEEDS to be CHANGED! After blocking a string like that one mentioned, you MUST be able to react, like immediately ducking (without blocking), jumping or start a string of yours. That move would still be safe on block, but you would be able to react immediately. Take Scorpion's [2,1,2] combo as an example (not on block). After the second hit, your opponent will last on his stun animation for long enough to be hit by the sword strike. But, if you interrupt the string on the second move (not landing the last one), you'll be on a perfect 50/50 situation, where you can move/jump/use any other attack while your opponent can react immediately by jumping, crouching or performing any attack.
3. NO MORE GUARANTEED THROWS AFTER A BLOCKED JIP. One of the most stupid things on this game is a blocked Jump-In-Punch. Every time you do a JIP and your opponent blocks it, almost every single normal attack is guaranteed. Yeah, this is fair, but THROWS BEING GUARANTEED TOO? If so, there's certainly something very wrong here. Your opponent must be able to evade a throw after a blocked JIP, but you also have to be able to create a blockstring with your normals. The blockstun time must be adjusted in order to make it PERFECT, so you won't be punished for a blocked JIP, neither will be on a HUGE advantage. Best solution I found to this issue is to make the JIP somewhat familiar to what they were in UMK3. In that game, if you just press up and punch and your opponent blocks it, your character would just gently fall down. But if you do a JIP and immediately press the button combination of one of your character's combos, your character will immediately appear on the ground, doing the combo you've just pressed. This might sound a little too goofy on today's technology and graphics, but would fix the blocked JIP issue for good!