Yes, yes yes! SOmeone else has this issue! I actually think the problem is his limbs look too tiny and are too low in his body (the curvature where the ribs would be starts BEFORE the joint point of his arms). I mean, if you take a look at the amazing splash art, the propertions there seem really, REALLY right. I don't know why the decision was made to have such tiny limbs (specially the hands) with such a huge head. It really looks like a baby instead of a full grown, fearing ancient being.
Surprisingly, though, the Ashen Lord skin doesn't seem to be so outrageous. I'm not sure as to what's going on... It's really a shame because when I saw the reveal and the splash art I was like "They did it!" and then when I saw the in-game model in pics and on the PBE myself I was like "I want to really like this guy, but my OCD just won't let me"
crosses fingers so Riot notices the thread and does some work
EDIT: Splash art for reference:
http://euw.leagueoflegends.com/sites/default/files/upload/aurelion-sol-banner.jpg