He doesn't have a lot of skill expression
being able to juggle axes efficiently to optimize the mana you're burning through is skill expression. not to mention being good at throwing them, reading opponents, etc.
does feel oppressive when good/ahead or useless simply due to the feast and famine nature of his kit.
any champ who snowballs does this. I'd hardly say it's faulty design, and Olaf is one of the few juggernauts who can go full tank and still be well off, and his Q poke/permaslow means he's not nearly useless as some of the other juggernauts when behind.
my only problems with him is his redundant steroids (AS on passive, AS on W -- the same problem I think Aatrox has between his P/R) and his E could stand to be more interesting. Thematically he's great, and as far as gameplay goes I consider him the most well-designed of the 'old' Juggernauts who haven't received an overhaul or were released recently
for example. Olaf has a very distinct niche as a more or less 'anti-carry' playstyle thanks to his high flat damage letting him run squishies down when his ult's up