https://www.youtube.com/watch?v=V4h9KN-fvmY

This video basically explains it all, for some odd reason in minecraft 1.8 if you have your settings maxed out your game will refuse to finish "downloading terrain" the solution is to turn your render distance down into the normal range

Here is what the launcher says while minecraft gets stuck on "downloading terrain"
[17:10:51] [Server thread/INFO]: Scanning folders...
[17:10:51] [Server thread/INFO]: Total conversion count is 0
[17:10:52] [Server thread/INFO]: Preparing start region for level 0
[17:10:53] [Server thread/INFO]: Preparing spawn area: 7%
[17:10:54] [Server thread/INFO]: Preparing spawn area: 16%
[17:10:55] [Server thread/INFO]: Preparing spawn area: 28%
[17:10:56] [Server thread/INFO]: Preparing spawn area: 41%
[17:10:57] [Server thread/INFO]: Preparing spawn area: 56%
[17:10:58] [Server thread/INFO]: Preparing spawn area: 68%
[17:10:59] [Server thread/INFO]: Preparing spawn area: 85%
[17:11:00] [Server thread/INFO]: Changing view distance to 32, from 10
[17:11:00] [Server thread/INFO]: coolgamerovr90[local:E:6818938d] logged in with entity id 205 at (13.5, 62.0, -86.5)
[17:11:00] [Server thread/INFO]: coolgamerovr90 joined the game
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at this point the client screen displays "downloading terrain" and starts playing in game music
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[17:11:44] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 44074ms behind, skipping 881 tick(s)
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at this point you get let into the game and all you see is a world with nothing in it, see the first screenshot
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[17:11:55] [Client thread/INFO]: [CHAT] Saved screenshot as 2015-03-16_17.11.55.png
[17:12:13] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 29607ms behind, skipping 592 tick(s)
[17:12:16] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 2891ms behind, skipping 57 tick(s)
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At this point you finally get taken into a playable world.
on slower less powerful computers the JVM itself will just crash