Let me talk about how Season 4 has utterly disappointed me.
The vision changes I have rather negative feelings about. Trinkets are definetely nice, scaling along the game at a suitable pace (though I have my doubts about the warding one), but Riot got carried over by the whole "vision war" thing, IMO; it's just gotten plain annoying. The fact that stealth wards can still be placed in a decently high quantity makes it so that the effects on invisible vision downright annoying; oracle's elixir hasn't rejoiced much since it's nerf back in s3, and now vision wards are plain in sight, making them nearly worthless since even with 5 hit points they're gonna go down pretty fast, especially since you can only put 1 on the map for your team. This leaves the lens trinket as the best option, forcing everyone to take that instead of utilization of mini-clairvoyance and free warding.
It's forcing everyone to actively take part in stressful thinking about ward positioning with the limits, and god knows how well that's gonna go with the teammates you can get. In season 3, the 10 players either used wards, or didn't, and just left that up to the support; it went just fine either way (unless one side did it and the other didn't, but that's still a problem in s4). It's gonna lead to a lot of team arguments about ward placing.
Speaking of supports, I have mixed views. I feel that the support's role of more common warding (emphasis on "more common" because I don't want to be misinterpreted), along with the jungler, has been diminished now that the ward limits apply to everyone, and it puts a lot of pressure on them; I feel Riot focused on that role way too much; I'm loving the new AP scalings on support abilities, why couldn't you have left that there and done some less minor alterations to warding? The support role would've been in a much better position with the new utility masteries, scalings and trinkets, but with everything else you've dumped on to them you're putting way too much emphasis into the role and not others.
Speaking of roles, the new camp has caused some heavy splitting of preference between the jungling champions; champions who are generally quick on their routes benefit, but slower ones suffer, favoriting specific champions. The warding limit has also diminished their role for scouting and roaming, meaning that they have to rely more on their team than their team has to rely on them, which makes it just as bad. Ganking hasn't changed much, thankfully, though trinkets are bound to put a direct stop to champions worse at it. But the worst part is the replacement of the gold items; philosopher's stone and kage's lucky pick were removed, and I can not, for the life of me, figure out why. Avarice blade is still there for offensive ad junglers, thankfully (and it stacks with spirit!), but options are now severely limited; the 3 new gp items are HORRIBLE for junglers due to the specific way they level up and operate, which does not benefit them in the slightest. Now, every jungler (mostly the slower ones) who doesn't use avarice is forced to rush spirit or wriggles in order to keep a steady gold income, otherwise they fall behind quickly in early game. Overall, the jungling changes suck so much that people are actually considering abandoning the role as a whole for a team.
Finally, One For All was stamped into the ground, in my opinion; Riot moved it to Summoner's Rift. Why the hell would you do that? Now people insist on lane occupation in the rift similar to typical 5v5 games, people expect you to be good at what you do, even when it's your 1st time playing said champion (making you able to play unowned ones was not a good move!), and traditional implications of feeding and flaming are abound. The game just feels like a traditional 5v5 unless your team is awesome enough to feel like rushing one lane again. The reason why it looked so appealing in the Howling Abyss was because everyone was doing the same thing at similar times in the same area, making it feel like a one for all havoc. But you're splitting the fun up for most of the game by keeping it on Summoner's Rift. Not cool, Riot.
Sorry, but I'm just kinda angry at how much this season has disappointed me. Granted, if anyone has a different opinion of it, I'm happy to listen.