The expansion doesn't seem worth it to me if they don't fix some of the vision issues, flanked units sometimes not being counted as flanked, teleporting enemies, getting shot at by enemies you hadn't seen yet, enemies shooting at you when you can't see them (not sectopod), or that one FUCKING thin man who spawns at the end of the anna sing mission (the one with the large fountains) in the FUCKING open but still has FUCKING high cover. Which bugs are you talking about specifically? I really enjoyed EU, but I've been waiting to see if they fixed the bugs before throwing any more money at xcom. Imo the ai is quite strong, especialy now that they have fixed the overwatch/flank bug. Alas they spent their ai budget on making awesome cut action scenes and voice acting i guess. The same thing that everyone who plays against the ai wants in any game. I'm curious, exactly what are you looking for in a higher difficulty if not more and tougher enemies?
The AI gains bonuses to its aim on higher difficulties, so yes, the AI cheats.