Wanted to sleep on my response to thoroughly give you a well rounded opinion. I still 100% stand behind the fact that it is a no fun mechanic. I am not arguing that no cards should instill frustration on the opponent, your examples being "Discord/Black Hole, Fire Shield, Steal, Phase Shield, Fractal, Pests, Pandemonium/Bonewall etc..." but in every single one of the examples you gave, the player using those killer cards at the right time can see exactly what problems he created for the opponent which creates "fun" and satisfaction. For the reshuffling of the deck you will use it on the opponent and if you did not use it with precog, you have no idea if it hurt or maybe even helped the opponent. It turns into simply an inconvenience for the other player in most cases. Dont get me wrong, I REALLY like the idea of reshuffling the hand mechanic but the inability for it to have the satisfaction of payoff is something that has kept countless other cards from becoming a part of the game.
Reshuffling, as said in the other posts, also has a double mechanic being that you can both use it on yourself as well as the opponent and this is really where all of my support behind the card lies. I simply think that it does too much for too little quantum in a color who's strength should not be having one of the top PCs.
You can think it is weaker than explosion and I guess that is your opinion but recognize that part of the theme of fire is straight destruction and as such they should have more efficient means of doing so. If you give a colorless PC to EVERY COLOR that is even close to comparable of explosion then it really ruins much of the uniqueness felt by each individual color. The joy of this game is knowing what you want your deck to do and combining colors and combinations to accomplish that, having all color combinations be more homogeneous is not a move in the right direction.(And I heavily suspect one of the reasons they are making shard changes)