An overabundance of CDR.
Seriously, Riot. They're are too many items with CDR. Some just flat out don't need it or have too much. Its annoying to buy some items because you overcap cdr making it less cost efficient. Or it makes some items too good. Essence Reaver for instance. Or the ease of which so much CDR can be obtained makes some champs flat out op, then those champs get nerfed, meaning if you dont build those items youre at a disadvantage, or if you play that champ different youre at a disadvantage. Many champs who had gone for a while in a balanced state simply become overbearing because they can easily cap out cdr in 2 items.
Im sure this is the millionth post saying this but yeah, there is too much.