SR is the same, just mostly revamped.
Biggest changes to it:
- Smite buffs were replaced by plants. These plants spawn at semi-set times in semi-set locations (imagine camps, but destroyed in a single hit, not necessarily spawning at the same time every time, and not necessarily always in the same location. These three plants are the honeyfruit (Restores a percent of missing health and mana on pickup), blast cones (launches you a set distance away depending on how you're standing next to it), and Scryer's Bloom (like an AoE Oracles that only reveals instead of disabling). Smite also heals you based on level and max HP when using it on a monster.
- The regular dragon was replaced by elemental drakes, which give a stacking permanent buff based on what one you kill. The buffs are similar to the old dragon buffs, with bonus AD/AP, bonus structure damage, bonus health and mana regen (out of combat), and bonus MS. After 35 minutes, it spawns an elder dragon, which is basically the exact same thing as the previous 5th dragon.
- Rift herald is a thing. It smashes into turrets, inhibs, and nexuses, and does a lot of damage to them. You get it by killing the rift herald and picking up its eye, then smashing its eye (it takes up the holder's trinket slot until then, and gives baron's recall to its holder until it's smashed). It sits in Baron's pit from 10 minutes to 20 minutes or until killed.
Runes were deleted, and masteries were reworked and renamed into runes. Some are similar to the previous iteration, but there are a lot of new ones as well. It has less total choices, but more meaningful ones (no more just "Do I get flat or scaling armor?" or "Do I get flat AD or armor pen?"). (Oh, and speaking of armor pen: It was reworked into Lethality, which is basically the same thing, except its effectiveness scales with your level).
Some items are gone, and there are new ones. Items also got reworked. Biggest thing is that if you rush IE and you're not Trynd you're trolling, as it gives no crit by itself anymore.
The level and IP systems were reworked. You can now level past 30, and every level gives you a champion capsule. This capsule contains one or more champion shards, which you can either upgrade for a fraction of their normal BE cost (40-60%), or you can disenchant for BE (Blue Essence - Basically it's IP except different). You no longer gain BE for playing a game (except from First Win bonus), and instead it's only through missions (basically free rewards you get occasionally when Riot puts them out) and the champion capsules. Basically means you get it all in a large chunk rather than slowly over time, although the rate is still roughly the same.
And, of course, lots of champions were added and reworked, and nerfed and buffed.