You have definitely missed a lot, a lot of bad, and very little good xD. The meta is currently in a clown show fiesta atm, double ADC bot, NO ADC BOT, as in Ziggs and Malz bot lane, or Teemo and Brand. AP MF "SUPPORT" doing more damage than the REAL ADC with actual AD items. AP Varus doing more damage than AD Varus.
WW new release is broken as fuck, as is every rework upon release( not my words, just the people playing him)
Turrets nerfed for LCS because "level 2 turret dives" are more entertaining to watch vs the balance of the damn game.
On that note, LOTS AND LOTS of LCS based changes. 10 bans to add "diversity" Yet still results in the same handful of champs that we have always seen, besides an occasional Kata.
Top lane is a complete snowball fest, you win level 4 basically, then continue to win the whole match, very little counterplay left, if you get behind, you stay behind.
Assassin reworks in an attempt to fight tanks, but didn't really do tooooo much, Vayne is still your best bet against a Naut xD.
Some jungle changes, like vision, some health glob plants, and more JG creatures. As well as Dragon rework, there are now different element dragons that give different buffs.
You've missed some new champs, and new reworks.
DO NOT PLAY RANKED right now, the match making is HORRRRRRRIBLE as is every mid season. However on that note, you missed solo queue being taken out, and premades ruling ranked, now we have solo/duo queue back which is nice, but we have to deal with AUTO-FILL instead, which causes players to steal lanes and auto lock or dodge more than ever, or they pick troll champs for the lane they got filled into, and then feed and AFK. Auto-Fill is very much so a BAD thing. It is making this game more toxic than i have ever seen. Not just flamers, but now people just take out their frustrations on their team since they got auto-filled.
Avoid Bot lane like i said, it's a circus show, and you will most likely get a auto fill support who is unhappy that they got support xD.