Put the summary of the bug you're having here

What I expected to happen was...:
The game was going to load and I was going to be able to play minecraft with the new features

What actually happened was...:
The game goes to the loading screen then crashes and goes back to the launcher.

Steps to Reproduce:
1. choose any version past 1.7.2 (including any snapshot)
2. click download and play
3. wait for it to download, you will see the mojang screen
4. the game crashes and shows the launcher
3. ...