The only cards which I think need a drastic rethinking are Pyroblast and Mind Control, because neither of those cards are just any fun to play against.
Pyroblast is unfun because for a great many classes there's just nothing you can do about it. If you had a rocky start against a mage but then went the rest of the game absolutely dominating them, it wont matter because if you can't kill them before 10 mana it's over. That's no fun, it's just frustrating.
Mind Control meanwhile has much the same problem. Against any class other than priest there's always those last-ditch moments where maybe you've been doing badly but you just got the 'perfect' minion to help, and suddenly the game is re-invigorated. But with priests that just can't happen, you're too nervous to play any big creatures late-game because you know they'll just get stolen and when finally you are forced to play them, well, they get stolen and you've lost without even having had a chance to fight back.
It takes an entire dynamic out of the match. It's just no fun.
Everything else can be annoying at times or can be frustrating, but can also be worked around. The Force of Nature/Savage Roar combo? Powerful, but it actually takes two cards to pull off and can also be prevented or mitigated via something as simple as a weakling taunt minion. Murloc War Leader? Annoying as hell, but murloc are weak on their own. Prevent them from building up numbers and you should be just fine. Leeroy? Sure he hits hard and has a low cost, which means rogues can do some truly crazy stuff with him, but again it takes effort and can be prevented and mitigated.
Even Ragnaros, who's an annoying SOB who probably should be cost more for how powerful he is, is still at least fair. Flood the board with cheap minions and suddenly that 8 dmg chance is picking off Loot Hoarders instead of doing anything useful. Or, y'know, just shoot the guy with a Big Game Hunter. I keep a pair of those guys in my druid deck for just such occasions (Since Druids lack good big removal otherwise).
Pyroblast is unfun because for a great many classes there's just nothing you can do about it. If you had a rocky start against a mage but then went the rest of the game absolutely dominating them, it wont matter because if you can't kill them before 10 mana it's over. That's no fun, it's just frustrating.
Mind Control meanwhile has much the same problem. Against any class other than priest there's always those last-ditch moments where maybe you've been doing badly but you just got the 'perfect' minion to help, and suddenly the game is re-invigorated. But with priests that just can't happen, you're too nervous to play any big creatures late-game because you know they'll just get stolen and when finally you are forced to play them, well, they get stolen and you've lost without even having had a chance to fight back.
It takes an entire dynamic out of the match. It's just no fun.
Everything else can be annoying at times or can be frustrating, but can also be worked around. The Force of Nature/Savage Roar combo? Powerful, but it actually takes two cards to pull off and can also be prevented or mitigated via something as simple as a weakling taunt minion. Murloc War Leader? Annoying as hell, but murloc are weak on their own. Prevent them from building up numbers and you should be just fine. Leeroy? Sure he hits hard and has a low cost, which means rogues can do some truly crazy stuff with him, but again it takes effort and can be prevented and mitigated.
Even Ragnaros, who's an annoying SOB who probably should be cost more for how powerful he is, is still at least fair. Flood the board with cheap minions and suddenly that 8 dmg chance is picking off Loot Hoarders instead of doing anything useful. Or, y'know, just shoot the guy with a Big Game Hunter. I keep a pair of those guys in my druid deck for just such occasions (Since Druids lack good big removal otherwise).