Huge changes to the pokemon formula since Pokemon X & Y, no longer as it's strictly battle and collecting focused (although still present) as they added variety of mechanics to switch things up a bit and to bring more variety in gameplay. Changes include:

1. No HMs
No longer do you have to carry around a HM slave (s). This has bothered me in the past games as I have to restrict 1 or 2 slots out of my party of 6 to help traverse certain areas of the world. In the place of HMs there are Poké Rides where you can ride pokemon interacting with them on the world map, some you may not be able to access until you've completed mission within the game.

2. Is it super effective?
No longer do you have to look up guides online (unless it's your first encounter) to tell if a move is super effective or not very effective against the pokemon you're up against. After you battle a pokemon once, the game will tell you what moves is super effective or not in the battle menu once you encounter the same pokemon the second time.

3. No Traditional Gyms
No longer do you have to battle your way through gym after gym to prove you're the best out of brute force.
There are 4 islands in the game, each of which are controlled by 4 Island Kahunas
To get to them you have to get pass Trail Captains and Todum Pokemon
Trail captain will give you quizzes, side quests to complete, and/or fight in traditional battles
Todum Pokemon. Basically typical pokemon you find the wild, but significantly stronger and have grunts that help them battle.

4. Rotom Pokédex
Typical pokedex, but with a face and personality attached to it.

5. Alola Forms
Basically different forms of pokemon you seen in previous generations. Either it's there physical form that is different and/or the pokemon's typing

6. Z-Moves
With a Z-Ring and a Z-Crystal you can use a pokemon's ultimate move once per battle. It's not like Mega Evolutions where it stays constant

7. QR Scanner.
You can now scan QR codes to get event pokemon

8. Battle Royal
A 4 player free-for-all where the battle ends after all of one's pokemon trainer's faints. They tally the win-losses of each trainer and the one with best stats at the end wins

9. Hyper Training.
Once a pokemon reaches level 100, they can go through hyper training which can improve a Pokemon's IV

10. Poké Pelago
Your PC Box now has functionality to it. It's like a day care sort of thing, instead of just depositing your pokemon, you can passively train them in the PC or have them search for items

11. Festival Plaza.
An online mode where you can battle other trainers and trade with them. You get festial coins for each interaction which you can spend on clothes, shop or upgrade your pokemon's stats. There's also missions you can undertake to get more coins.

12. Night and Day phase, New Pokemon
Pokemon Sun goes the traditional time route while Moon does the opposite. In Pokemon Moon if you're playing in the daytime, the game will consider it night time in-game. Some events also play out differently like different Totum Pokemon on the same island/trail
In traditional Pokemon fashion you can only get some pokemon in each version so trading is required either with a friend or if you own both versions. Also some pokemon evolve differently in each version now.
I'd say some of overall models of new pokemon are better looking than the last batch in previous iterations of the pokemon series.

13. Auto Run
Your run is as fast as a bike now, and it has unlimited use. You can now move in all directions instead of the traditional 4 and it feels very fluid

14. No Rod
Fishing is now dedicated to specific regions in the world. You cannot fish wherever you want anymore.

15. Photo Taking
You can now take Photos of pokemon in the wild.

16. Team Skull and Aether Foundation
Team Skull is the new antagonist group like Team Rocket, but they have a new style to them as they try act gangster-ish with their animated hand gesters/movements. They have more personality and have a darker tone to their backstory and mission.
Aether Foundation is the opposite of Team Skull as their mission is to cure injured and hurt pokemon. The group is also conducting research on the Ultra Beast (Pokemon) which is a good mystery story in and of itself.

17. Graphical Upgrade
Game looks better than the last, although there are some pixelation around the edges still. Models look more realistic than before, and the battle animations are more visually impressive. There are some framerate issues on 2v2 battles for some reason, but then again I own the launch 3DS. You may not have the issue if you own the New 3DS? It's a turn-based system so it doesn't really matter much in terms of gameplay, but the slow down is noticeable

18. Pokemon Refresh
Similar to Pokemon amie but with more grooming options

-Returning mechanics:
Pokebank return, you can now transfer all your pokemon to Sun and Moon
Clothing Options: Although more options are available, it still feel very limited.
Mega Evolutions return, but none for new pokemon from what i've discovered

Overall, love the changes to the traditional formula as it gives the Pokemon Series a nice refresh and is more streamline to play.

Great game. I spent over a hundred hours as of the release of the game in November. It took a lot of mechanics including move's attack power and leveling up ways and made them a little different. There are multiple ways to level your Pokemon, encounters are different as well, and it feels a little fresher. I had a lot of fun.

A downside is how childish it can be. Don't get me wrong, I know the target audience is children but I personally grew up with the game and one day want to see something new. I can't wait to see what Nintendo comes up with next.

I have played every Pokémon game cycle and I'm not trying to say this is a bad game because it isn't.

My problem with it is the story, it didn't draw me in like the older games, I don't know if it was the change of the gyms to trials or it was just little changes but overall it's the first I haven't even finished because 10 hours in I feel obligated to play instead of drawn into the game like previous games in the series.

A lot more forgettable of a game than before. I didn't find myself playing as much as the previous games, even if the visuals were great this time around. I've never been one to invest a lot of time in pokemon breeding and things like that because I find it to be too tedious for my lack of game patience but I've always managed to still have fun building different teams and constantly coming back to play my game. This time around though, I felt like everything was far too linear? Not a lot of places left exploration/discovery since you are already kind of told where to go, what to do and what you'll find. This was probably to accommodate all the newer fans but it definitely felt more of a game for them than for an older fan like myself. And I was definitely disappointed in the removal of streetpass/spotpass features. You were forced to hang in the festival area to do any kind of interaction, and then you had to collect tickets to do certain things, I kind of just gave up on that.

This is a great game, though definitely a departure from previous titles in the series. I enjoyed it, but it's interesting how much they changed up the formula. I really love how they simplified the format of the HMs and show you which moves are super effective. I'm sure the hardcore don't need this, but if you're a casual like me or using a dual-element attack against a dual-element Pokemon this is a real life-saver.

Also, I love how they removed the Pokemon Ami games in this version, I spent way too much time farming cupcakes in Gen 6. :)

It's an ok game. wish there were more character variability within game. Lots to explore and way more advanced, in terms of graphics, than previous series.

Great way to breathe life into this franchise, even without the typical gym challenges and region exploration, this game is pokemon through and through. Very open world feel to it and is the closest game to and rpg in the series. New story characters, pokemon, there is something for everybody in this game. Must buy for anyone who has any interest in pokemon!

Purchases this game for my daughter's upcoming birthday, but I also own a copy myself and my husband owns the Sun version. I love the game. I think they did amazing with it like every pokemon game, but this one is my favorite so far. Anything about the former pokemon games that I might not have liked they fixed in this game and it all works out perfectly. This game actually came in early and was in perfect condition. I can not wait for my daughter to open this along with her new ds on her birthday!