Where to even begin... I for one am truly shocked that this is actually true and that he would betray Dortmund like that and push for this transfer. This is very VERY disappointing.
1. Not an even slightly respectable move on his part. I used to applaud him for being one of the more loyal youngsters in football and I thought he had his priorities straight and some ethical boundaries, but this is just a completely horrible way to repay Dortmund.
2. Klopp himself was having so much trouble keeping his cool when commenting on it, and I don't blame him at all. This must frustrate him a lot as it'll be hard to rebuild Dortmund after a loss like this.
3. One transfer may not seem that important, however it's more of a symbolic one than purely literal. Gotze was the icon of Dortmund's rise to European power and he was the idol of the team. How lost will the club be when that icon is gone and the future star player they raised is moving to their rivals. He went from leading the next generation to success to jumping ship. Dortmund will now be viewed as more of a selling club. Along with Gotze, there will be several other players to leave such as Lewandowksi, Hummels, Sahin, and maybe even Gundogan. There is a HUGE loss of hope after this...
4. Bayern have not only secured the signing of a phenomenal youngster who'll contend for the Ballon D'or within a few years, they've successfully sparked the collapse of their main domestic rivals and are going to rise up phenomenally with young players like Shaqiri, Kroos, Martinez, Gotze, Muller, Alaba, etc. all under the guidance of Guardiola. This means the Bundesliga will definitely be a monopoly for many years to come with no competitive title race. It's even possible that they could go on to dominate in Europe continuously with all the funds they get.
5. Gotze looks set to be the focal point of a 2nd false 9 experiment at Bayern and Germany. Will he ever reach the levels of Messi? No. He doesn't have that level of brilliance and the sheer talent of a once in a century player. He'll have his own style (I presume he'll be more on the playmaking side of a false 9) and no doubt he has the potential to become a truly world class player.
6. He will always be remembered for this move. It's quite a memorable thing to do and the only way it'll be played down in the future is if Dortmund stoop low enough for people to forget that he transferred from rivals on an equal level, not just a small club.