Rengar: Was definitely in need of a nerf, but they may have gone a tad bit overboard on this one. The loss of the base AD on his necklace was almost definitely unnecessary, but only time will tell I guess. Don't own him, never played as him, and before you say "Oracle's or Vision Wards", Oracle's is really not viable on anyone but support or jungle, and keeping your lane covered in vision wards to protect from all possible gank/escape angles is just too damn expensive with how long his stealth duration was previously.
Ezreal: Played against Ez quite a bit, although only played as him for the first time this past rotation when he was free and bought him a couple of days ago. I can honestly say that I rarely lost my lane to him, and when I did it was usually because of an awful support, or I just did something incredibly stupid. In any case the only time his attack speed debuff was a real issue was when he was already ahead, and in that situation he should have the advantage. If enough people really thought it was that OP, I could see halving the debuff, but removing it completely seems like your standard knee-jerk overreaction.
Sona: "Let's make the squishiest champion in the league squishier than a melee minion". Really Riot? If she needed a nerf it's her poke damage that needed it. All you did was give the opposing bot lane an easy First Blood if Sona is ever picked again.
Skarner: I can understand the nerf to his ult, provided of course that the same thing was done to all other ults that act similarly, such as Darius' among others. I don't have any strong feelings about his shield one way or the other. On the one hand it'll make getting away from him actually possible, but on the other it screws over his jungling potential.
DFG: Really disappointed on this one. I can see how the item could be considered op considering it wasn't all that difficult to get it above 50% by end game, but reducing the base damage by 10% and completely removing the CDR? Seriously? This was one of the few items that kept lb from completely falling off past mid game and now it is almost worthless to her, or at the very least horrendously overpriced for what it delivers. And as has been already stated, a good number of other APs which used to include this item in their core builds are also up a creek without a paddle.
Ward Skins: As a rule I don't buy skins, I'd rather spend my RP unlocking more champs thank you very much. But even if I was inclined to spend money to buy skins, I sure as hell wouldn't be willing to rent them (even if they can be rented with IP).
New TT: Don't see why you had to completely replace the old map with a new one that plays in an entirely different manner. Didn't play the old one much, and will probably enjoy the new one, but that doesn't change the fact that you've given a big ol' middle finger to the hardcore 3v3 community.
The Rest: Didn't really care one way or the other.
Not QQing here, just my initial impressions on what we've been told so far. maybe after playing with these changes I'll change my mind but for the most part I felt that most of them were unnecessary or overboard.