Need Pokemon advice! Last Pokemon I played was Pokemon gold.

[ImmortalHelixFossil]

Right now I am a happy owner of an 3DS. I am looking for a great Pokemon, the last Pokemon I played was Pokemon gold on the Gameboy colour. 

I need some great advice, which Pokemon should I buy? I am looking for a game with a DS or 3DS format. 

What's important for me:

- A lot of different Pokemons that can hook me for weeks.
- Great story, one that makes me read what's happening instead of raping the A button.
- A lot of side quests or missions (if that's possible)
- Something to do after I beated the Pokemon league, and that's interesting
- Gigantic map compared with Pokemon G/S/C


PS: I just read about Pokemon HeartGold/SoulSilver, and I am looking for something new. I'll definitly try them later =)