Let's put the hate to rest shall we? This game is NOT related to the Stadium series and doesn't pretend to be.
1. Why does the battle mode lack options?
It doesn't. Compared to Ruby & Sapphire it more or less has the exact same battle options.
2. Why do I need to have a copy of R/S and a GBA to do multi-player battle?
What Colosseum owner doesn't have Ruby or Sapphire to begin with? And as for why you need to link up, well you have to do so for the R/S do you not? Same thing.
3. Where's the mini-games?
In POKéMON Channel. Did R/S have mini-games? No. Why should Colosseum?
4. Why the low amount of storage space and no Stadium-like PC info?
Those things are in POKéMON Box. Colosseum isn't meant to be a storage device as there aren't many POKéMON to catch in-game as it is.
5. So you're saying...??
I'm saying that if it was another Stadium it'd have been named as such. Instead it's more or less a 3d version of the Gameboy series of games. Sure the story mode doesn't have badge collecting or "real" capturing, but if it did then would you still be comparing it to the Stadiums? I don't think so.