The W London is infamous for probably having the worst overall reception amongst Flyertalkers. The main things I'd point to are:
- Really impractical rooms without actual bathrooms, a desk which is attached to the sink and a shower which floods the area around the bed (I believe this is all room types up to premium suite)
- Terrible, can't be bothered service
- "Legendary" bar which should be avoided at all costs
The W Istanbul meanwhile is just a dirty, smelly place for prostitutes to hang out. Good location though!