I absolutely love the "spin-off" games. (I HATE CALLING THEM THAT, but it's true)
It is likely you could, too, but it depends if you don't mind a lot of mechanics being different from the original games.
Answers :D :
I kinda spoil things, but we all know you have to defeat the villain team at the end.
Would it occupy me?
If you care enough, for a good 6 hours plus.
What kind of customization can I do? (Name, looks, etc.)
Absolutely nothing besides the name and Pokemon nicknames. Do not expect things like X and Y. At all.
What is the storyline?
Picks up a few years after Colosseum. You are a kid, whose Mother(Lily) works at a Pokemon Lab in the Orre Region. The villain team from Colosseum, Cipher, is starting to make "Shadow Pokemon" again, and you are given the Snag Machine to allow you to "Snag" their Pokemon, in battle. You ultimately defeat Cipher, making friends and enemies along the way.
What do you get to do?
-Snag Shadow Pokemon from Trainers and Cipher Peons/Admins/Leaders.
-Explore Orre.
-Battle in colosseum battles.
-Catch Wild Pokemon from PokeSpots.
-Listen to Miror B's theme.
-HAVE FUN! :D (if you get it)
Edit: Oh, Yeah, your starter is a level 10 Eevee. You can evolve it any of the first five ways you want.