AEN took an "HD" file and made it 170 megs. Even if it's an mp4, they just don't look that good that way. The compression gets too high, and you lose a lot in the bitrate. Because the source was over 400 megs, they are coming from fairly high quality, but they are just pushing it too far. Order used HD sources for Gurren Lagann, and they were cutting it tight with 238 meg mp4's.

AEN has improved..a bit in their translation, but the translator has frequently defended himself saying that the only reason for doing this is to learn Japanese. I am not aware they use QC at all.

Spelling errors are common, the language is awful, and I often have to take time to figure out what the hell they were trying to say. I'm not fluent by any means, but after watching all this anime, you gain a pretty good idea what a word or phrase is analogous to in English. AEN subs rarely meet that.

It's gotten better, but when you're going from shitsubs to trashsubs, that's not saying a whole lot.