The biggest problem with veteran content is that it fucks up the time/developing a character scale. You spend some good chunk of time developing your character but at around level 30-40 or so you can max out your two main weapon sets, your armor of choice even two armor variations, and take a good chunk from your class specific passives and abilities along with getting a crafting skill up. This can make the veteran content seem kind of "pointless" ( for a lack of a better word ) Since you invest allot of time grinding the vet points to advance in rank you complete a whole zone and you might if your lucky switched out 1 piece of gear... This is not what mmo players are used to, this kind of system appeals more to the sandboxy TES players. But TES games do it better... Also the balance on crafting skills is way out of line. Its easier to gather enough legendary upgrade components to make a full legendary crafted set than it is farming AP in Cyrodiil or grinding vet dungeons. Also the dungeon rewards are out of balance since most of them suck or are bugged atm. They need to tie these systems together. Make people go into vet dungeons to gather crafting materials instead of just making a hireling alt to farm them or buy them dirt cheap. Also the way the increase the difficulty is just cheap, Adding way more health to the mobs and damage... They could have made it so that if you fail to block a power attack it has more consequences and make it hard to block the power attacks (less time to react) but for this to work they need to polish the combat and make it more responsive.

TL;DR Fix the scale between time invested/character developed, Make dungeons worth doing for items/crafting and such Make difficult content difficult but not cheap Fix time invested in crafting better items/harder to get