I don't think that Arcane Trickster is that bad, at least relative to Rogue in general (Which suffers overall when played as a pure class)
The only thing I'd wish for is for Magical Ambush to be received earlier (It's not PHB friendly, but Larian did make Dragon Sorcerers get their flight at level 11 instead of 14 for example) so you can get it alongside a decent Wiz multiclass.
With of course, global Rogue change for Sneak Attack to be once per standard action instead of once per turn (Allowing them to benefit from Haste in a way comparable to literally every other Martial that can get their multiple attacks from the extra standard action)
Outside of those things, the subclass is fine. You have 2 different ways to play it;
- You can be just a standard Rogue but with a few extra things like Shield, Fog Cloud, Darkness to provide utility and defence.
- You can play a Gish build where you utilize all the neat items that provide bonuses for using spells and melee (Where you can activate many of them with a cantrip and then use a sneak attack with an off-hand weapon to deal your damage) alongside scrolls and whatever your Wizard multiclass enables.
