I left league at the end of 2014 (october) , what major changes has happened

Tank meta = Current meta Cinderhulk (jungle item enchant) is/was really big (tanky CC jungs like Sej have a 90% ban rate). People would take smite top lane just to build Cinderhulk on tanky toplaners, in addition to having a Cinderhulk jungler. But it was recently nerfed so we'll see what happens?

The best thing you could do is read the patch notes or watch patch note videos. There's lot of people that do condensed patch note videos. I want to say blakinola (?) does some good ones, but I could have the wrong name in mind.

luden's echo has replaced deathfire grasp ad assassins have fallen out of the meta due to too much cc and too many tanks

Jungle changes are the biggest ones... Dragon no longer gives global gold. Now gives a stacking permanent buff that gives successive benefits at each rank before rank 5 which doubles them but only lasts for a few minutes (getting dragon 5 is basically a win condition now; I've only ever seen one team fail to win during the duration of the buff, but they did win shortly thereafter because they wrecked the opposing team's base and then took baron and won).

Smiting the big monsters in each camp gives a buff. Gromp (new monster) gives thornmail-like damage return. Blue Buff gives mana. Red Buff gives health. Wolves give a sight ward thingy that follows enemies that invade your jungle. Raptors (replaced Wraiths) tell you when you've been spotted by a ward and give you temporary true sight to kill it. Krugs (replaced the golems) grant a stun on monsters every few attacks. Jungle routes can now start at Gromp, Blue, Red, or Krugs.

Smite has 2 charges with a cooldown between them of 15 seconds and a recharge time of 75 IIRC.

Baron now gives a massive siege buff to minions near your champions (buffed cannon minions outrange turrets).

There are now items that can be bought to augment smite, several of which allow it to target players (for reduced damage). These items can then be enchanted (like boots) to correspond to different builds like tank, mage, fighter, etc.

Inner turrets now have a continuous laser that slows movement and I think AS of whatever they're firing on (implemented to reduce power of split pushing). Side inner turrets also grant a Malphite-like shield to nearby allied champions.

Currently the meta is considered the "Tank Meta," as it is not uncommon to see two or three 5k HP champions on a team later in the game. In practice, it's basically the "Anything" meta because just about every champion is viable at this point. The game is actually the most balanced it's been in a while.

Mana and health regen items got reworked to be %regen, not flat MP5 and HP5. Morellonomicon is good now.

DFG got removed and there's a new item called Luden's Echo which is basically Statikk Shiv for mages.

Few new champions, not gonna check to see which ones came when exactly. Azir (zone control ADC-by-proxy mage that can resurrect turrets for a short while), Bard (roaming support that has an AoE Zhonya's as an ult that can hit allies, foes, and even turrets and monsters), Kalista (ADC that can pull around their support and can hop around, kiting better than Ashe and has better objective control than Smite on her E), Rek'sai (burrowing jungler that can detect movement of enemies even in fog of war and over walls).

Tristana got a rework, Ashe got a rework, Sion got a MAJOR rework, Ryze got a recent rework and is still recovering. Veigar's E no longer instantly deploys. Zed can't instantly teleport back to his ult's shadow.

Oh yeah, and Urgot is viable. Seriously.

she's still easily bullied early game but if you have the skill to go even or even win lane with her then she has and always will be op.