After poking around on the wizards site, I have noticed one of the major issues right now is the post-Mirrodin block reaction to the addition of the Human class. This is not the big picture however. The clarification of Race-Class classification system of sub-types is what led to the development of the Human class(race) in Magic.
For most of you rookies this maybe nothing worth noticing. You may find it a tad odd that a human class is even necessary in a fantasy based game. But for most of us Casual Players, this will have at least a slight impact on not only our cards but also our knowledge of some of the rules. Type 2 play will remain unaffected for the most part except the base set. Type 1 and 1.5 will feel the impact the most.
The issue arises only when dealing with older and their reprinted cards. In the old sets, many creatures came with only one creature type. The most notable exception to this rule would probably the 5 Elder dragon legends. In more recent sets, many creatures expanded into multiple creature types. This was largely related to the fact that many legend cards also have an additional bit on them that say "This counts as x". For example, Ertai, Wizard Adept has the clause proclaiming his Wizard class.
In Mirrodin, since humans are no longer the only dominant species and with the introduction of the race class classification. The powers that be at Wizards of the Coast felt that they needed to add more oomph to just simple soldiers and clerics. They needed to give them the human subtype in order to differentiate from a goblin soldier versus a human soldier.
This of course has been met with mixed results. I personally reacted in a physical display of disgust with the opening of my first packs of Mirrodin. I thought it all was rather silly. HUMAN as a subtype? With all the different types out there including some memorable one time shots like Nightstalkers and Elder Dragon Legends. It seems a little weak and boring to bring normal humans into the fray. Another thing that bugs me about the cards is the fact that many times in magic, creatures are sacrificed to pay costs for different things. It's ok when you have to sac a goblin for goblin gernade or a cleric for Scion of Darkness. But I would feel a bit funny sacrificing humans on my way to victory. I hope many of you out there would agree with me on this. Though, these aren't the biggest impact on the game. The problem arises about what to do about all the old cards that need to have Human added into their subtypes? I believe there is a poll at the Wizards site at the moment to take feedback about this issue. Of all the solutions to this conundrum I voted for a rewording of all cards that need it and not only reprinted ones. I believe that is the anal part of me needing a clarification of all cards just in case I decide to abuse them for future purposes. I have heard both sides of the argument from live people around me. I personally do not browse through many other websites on the subject of Magic. This one in my humble opinion is one of the best if not the best.
But I digress. We go back to the issue at hand. The introduction of the new system is Wizards attempt (according to their PR website) to make the game better. It goes along with the color pie changes and attempts to streamline the game. One big aspect of the game are the creatures. Two favorite types of creature decks are tribal and theme. In this way, the new offering of the classification types does make it some what appealing to the casual player.
With any major change, time has to be given to see the net positive affect. You can't fully judge a president until about 20 to 30 years after his presidency to be fair to him. One thing is for certain though, whether this change is a net positive or negative on the game, it can not be taken back.