For years, the entire community (and critics as a whole) could agree on one thing, and that was that mist energy was a frustrating business. As a F2Player, I'd constantly be worried about leaving the game (and losing my mist as a result) or of how much profit I was making per mist energy spent. Instead of having fun and actually exploring the clockworks, players simply grinded through FSC over and over again until they realized just how boring it was and leave the game. If you became tired of that, you only had three options: leave the game, play LD, or merch in Haven. I opted for the first option about a month ago, and only returned when this update was announced.
First, the pets: Well, they are what they are, pets. Not just any cosmetic pets, but ones that you could feed your useless materials to. Minerals also play an important role in the game, instead of just being collected and deposited in the arcade. A much needed material/mineral sink. Now you actually get excited when you find 4*-5* mats. Also, you have the attacks/buffs/debuffs of your pet at your disposal, encouraging more teamwork and augmenting playstyles.
The revival system: instead of playing 5 CE with every death and then a rapidly increasing fee to pay, you have life sparks and emergency revives. Emergency revives are completely free, and you receive one with every level that you progress through. Amazingly charitable... Until you realize that after you die a second time, you'll need to use a life spark to revive. Your party members cannot simply give you 1/2 of their HP to get you ticking again. Life sparks are required, and you won't receive any drops unless you get off your butt and start killing monsters once more. But never fear, life sparks are just as common as tokens, and you'll never run out of them unless you really, really suck at playing the game. Even if you do run out, you can just leave the party and try again someplace else. You don't have to worry about the lack of mist, hooray! But if you do need to buy life sparks, they are 5E apeice. Still pretty nice, considering that the old system worked like this: First rev, 5E. Second rev, 10E. Third rev, 20E. Fourth, 40E, etc etc. So the revival system is quite charitable, in comparison to the old.
Crafting: To all those who used to play SK, they'd wonder "If we don't use CE anymore, then what do we use to craft gear? The answer? Orbs, of course! Instead of paying CE for items, you have to use orbs. And what are orbs? They are used to craft items of a certain level, and only that level. CE was universal, but orbs... Aren't. You'll need certain orbs for certain levels of gear. And where do you find them? Basically anywhere, and at a rate that is quite low. Low, but not too low that you'll be forced to pay Energy for them. Different orbs drop at different levels, with the 3* orb being found in T2, etc etc. For those that complain about these orbs, I have three words for you: Deal with it. Firstly, the orbs are quite easily farmed, and even if you aren't looking for them you'll find them. I've been playing T3 and I have 16 5* orbs. No problem to find them, no problem at all.
Mist Energy Removal: Ahhhh, undoubtedly the best part of this update. Finally, the mist system that everyone hated is gone! Gone, hoorah! And yet.. Amazingly.. There are naysayers. Some even want the ME/CE system back, and why? Because of the Forge.
The Forge: Yes, this is the certain part of the update that divides the entire community. There are two sides, those that proclaim that the forge is an abomination that must be expunged from the game, and those that think that the forge is a necessary evil. I take the latter side. First, I should explain what the forge is: instead of leveling up automatically with heat like we normally did, you have to use the forge to progress to the next level. To power the forge, you'll need heat crystal thingies that operate in the same way as those crafting orbs do. If you are leveling a 4* item, you'll need 4* crystals, which you will have to find in the earlier levels tier 3, and if you are leveling a 5* item you'll need to progress deeper in T3 to find. The crystals aren't that rare, especially if you know which depths you need to go to. But you need plenty of them if you want to have a 100% success rate of leveling up your gear. There are three differing amounts of crystals that you can deposit, and each gives you a certain success rate, which is normally 20% for the first amount, 70% for the second amount, and 100% as the third amount.
As if to make up for the annoyance of the forge, you have a chance to receive special rewards when leveling up your item, whether it be damage, skipping two levels, or receiving a forge lockbox that requires no key (you can only receive that bonus if you deposit the 100% amount of crystals). These bonuses can really help make your equipment more powerful. For those that constantly whine about how many crystals they are receiving, you are either in the wrong tier, are playing at too low a difficulty to get any good drops, or simply keep trying out the forge at 20%-70% success rate, which is what you should never do. Don't forget that if you replay missions, you won't find as many crystals/orbs/life sparks. Also, remember that developers need to eat, and make a bit of money too, so something has to replace the ME/CE system, and that is the forge. If you know how it works, you'll just understand that it is a necessary evil, and actually can be very rewarding. You can't expect to be spoonfed, though. You simply cannot have CE/ME being removed without a sacrifice, and that had to be heat.
Difficulty levels: Yes, the long awaited difficulty levels! Now we have three levels to choose from: Normal, Advanced, and Elite. Each level increases the drop rates, crown payout, and most importantly, the HP and Damage of mobs is increased. With each difficulty level that you decide to adventure on, you have to remember that the difficulty level between Normal and Advanced isn't all that much, but the drop rates are.. . Uncharitable on Normal Mode. On Elite, you'll definitely notice that the difficulty level is actually challenging, especially with enemies like dust bunnies and scarabs. Fortunately, the crown/drop payout will definitely show if you play on elite.
Reviving a dying game: As Neodasus pointed out, there didn't seem to be anything to do once you hit the endgame, unless it was to play lockdown or just play FSC over and over. Besides this, the game had just become too easy for those that had become experienced with the game. Twiddle dee dee, twiddle dee dum, I could play any level while in a coma. The elite mode changed that. The arcade was also more dead than Michael Jackson, and the update changed that. Heck, now I play on Arcade mode most of the time, simply for fun, the droprates, and the coop. Also, the pets have given us a new way to play the game, adding a lot more possibility to the gameplay.
Our playerbase on Steam alone has TRIPLED, as Mtax pointed out:
"Look how it was before update: http://s20.postimg.org/s88lrinst/top.png
How it is now: http://store.steampowered.com/stats
All of these aforementioned updates were suggested by the community, save the forging system. The devs listened to your suggestions and masterfully delivered, and now all you can do is whine about it.
When it comes right down to it, the issue of the forge is an irrational one. People on either side have their rational arguments, but barring very few people, they won't be swayed to the other side. The fact is, there was a subconscious connection of effort to reward when you raised heat enough to fill the bar and it leveled with a flash and celebration. It was something you put work into, and something that you could very clearly see the payoff of. Now that you have to forge it, the subconscious connection of effort to reward is broken, due in part to the fact that you have to rely on random fire crystal drops. It's basic MMO compulsion 101, and I'm surprised that OOO might not have game designers that consider things like this.