The new stealth system is horribly broken. Even with the feat "Stealthy" and maxed hide and move silent, monsters can detect you from the other side of the room, and worse for rogues, it tends to aggro everybody else in a wide area.
It is almost impossible to land a backstab, which requires luck or a failed bluff roll more than anything else (forget about patience, timing, and positioning), and forget about stealthily sneaking around the mobs, like in the quest Stealthy Repossession. Even if mobs don't see you through doors (a bigger problem now than ever), they can quickly see (or hear, or whatever) right through stealth.
The old system was fine. Too many changes just for the sake of change. Thanks for taking my favorite class from me, Turbine.