Is there any major things that are in Emerald, not Ruby?

Chinchou will evolve
Mew will learn ancient power and stuff
Change fire punch to thunder punch
The only person I can't think of is blue sister in pallet at about 3pm
Hope this helps :D

The Battle Frontier and you can catch Groudon and Kyogre.

Yes you can cach a sudoowoodoo and a smergle.
Also you catch Groundo and Kyogre and Rayquaza at level 70
Archie and maxie are in the game.
Wallace is the champion and there's a diferent gym leader.
Did that anser your queestion?

You can catch Rayquaza before the PKMN Leauge.

1. Yea you can catch both kyogre and groudon in emerald you can only catch groudon in ruby 2. The national pokedex 3.extended safari zone { johto Pokemon in section they were working on { must have beaten elite four first} }
4. The Battle Frontier Instead Of the battle tower 5.team aqua and team magma both do their diabolical scheeming in emerald 6.instead of steven being the champion wallace is the champion

thats all that I can think of right now

DARK LATIAS

Yes off course.
1.Battle Hall
2.Battle Tents
3.Battle Frontier
4.Faraway Island
5.New Champion
6.Upgraded Safari Zone
7.New Deoxys etc...

You can Catch Mew and the Battle Frontier.Groudon and Kyogre.Plus,Natinaol Dex and Jhoto Pokemon

You can catch groudon and kyogre and wallace is the champion your rival isn't enter sootopilis has a different gym leader and the twins at mossdeep have 4 Pokemon instead of 2 and there is the battle frontier and you can catch sudowoodou and there is match call and there is walda in rustboro and some pepole say different things and that is it. PS:sorry if there is no periods :(

1. You can catch Rayquaza before you beat the Elite Four, and Groudon AND Kyogre after you beat the Elite Four (All are level 70...)
2. You have access to the Battle Frontier instead of Battle Tower (Battle Tower IS part of the Battle Frontier; just some upgrades...) You can also go to Trainer Hill (North of Mauville), and there Battle Tents in the 3 towns that the Pokemon Contests used to be in --Besides Lilycove-- and in Lilycove you have access to all four types of Pokemon contests for the price of one.
3. In the desert there is this tower that you get one of the two fossils at the top and after you beat the Elite Four you can go to Desert Underpass (in the Fossil Maniac's house) where you obtain the other fossil you didn't chose.
4. After you beat the Elite Four, you have the choice of having the chance to catch either Lati.
5. There is a berry blender master in this game where you can blend pokeblocks with him- he is very good and never misses- you can make awesome pokeblocks with him. Anyway, you can find out when he'll be in Lilycove by watching the TV for any news...
6. There is this person, named Scott, that follows you around. He's the one that introduces you to the Battle Frontier.
7. Instead of the Trainer's eye program in the pokenav, there is a match call program where you can call trainers, or trainers call you.
8. You can battle Gym leaders in a double battle after you beat the Elite Four. Also, some of their gyms are different and truthfully, more difficult...
9. Some pokemons' ability has a second effect (Magma Armor- the number of steps it takes to hatch an egg is halved. Swarm- the cries of Pokemon in the background can be heard more often. Lightningrod- more trainers will call you on match call more often. --Those are all I know...--)
10. Juan is the leader in Sootopolis while Wallace is the Champion. But, the true champion, Steven, can be found in an added section in Meteor Falls after you beat the Elite Four.
11. Both Team Aqua and Magma do their evil schemes and you have to venture through both their hideouts...
12. You can get the National Dex and once you do so, you can catch certain Pokemon that isn't originally found in Hoenn: Sudowoodo and Smeargle in the Battle Frontier, Ditto in Desert Underpass, and quite a few rare Jhoto Pokemon that is found in an added part of the Safari Zone. Also, when you complete the Hoenn pokedex you can choose one of the Jhoto starters and when you (somehow) complete the Jhoto pokedex, it is said that you can choose one of the Kanto starters. If you can't, then just trade from FR/LG...
13. You can crush berries into berry powder in this game.
14. There are Move tutors throughout Hoenn.
15. There are different people who are willing to trade different Pokemon for different pokemon. For instance, in Pacifidlog, instead of a girl trading a Corsola for a Bellosom, there is a boy who would trade a Horsea for a Bagon.
16. Altering Cave is on Route 103 after you beat the Elite Four.
17. The Trick House challenges are different.
18. After a certain amount of battles with certain trainers you can obtain rare items, like after 5 battles with Dragon Tamer Nicolas you can get the Dragon Fang.
19. There are some added trainers, and some trainers are different and in different places. Like, on route 104, rich boy Winston and lady Cindy swap places and in Littleroot instead of a girl in front of May's house, there is a boy and in your rivals house there is a little girl. Not to mention, your clothes are green in this game.
20. And, a BIG difference is that there Pokemon animations.
... Sorry that this is so long, I tried to figure out the differences I noticed along my journey. Please rate this answer by accuracy, completion and length. Hope I helped!