Not sure on percentage, but it's worth it. The only downfall is you have to do everything manually. There's no DexNav and so far as I know, no money cheat. Those two things would make this perfect once it's finished.
Personally my only problem with it is that it's still unfinished. It's the only issue with these types of games really. They're so good, but when they're new it takes a lot of time and patience if you want to play the full game. It can be difficult, but it's wish it in my opinion. Nothing like Emerald Imperium though.
Don't think there are Megas yet. You can't breed wild Pokémon, only ones obtained through certain quests. I recommend you save before special events so you don't accidentally miss catching a hybrid. I missed the one in Trackless Forest because I didn't... You can farm the trainer in a few of the Ranger Guilds for money. Perfect if you pick Lucario for starter.
All in all good game. Could be improved, but I'm sure the finished product will be much better.