A solid outing; generic done well.
The Scroll Thief covers much of the same ground as the previous Adventurer's League title, "The Courting of Fire". The same antagonists are involved in yet another book theft from the library, and the party must pursue them to a wilderness location for a showdown. It also covers some of the same territory as the next module, "Drums In The Marsh", featuring a trip to the Twilight Marsh with dragons and (possibly) lizardfolk. A group playing the entire first AL season may find this repetitious; the intention presumably was that most players would only play one module out of each set of two or three releases in this season, and the repetition ensures that key elements will be encountered even if modules are skipped.
That said, on its own merits this is a decent module. The investigation phase features a variety of well-fleshed out characters and interesting interactions, developing the worldbuilding of Phlan in entertaining ways. A couple of the combats feature interesting foes that break out of the "thugs, undead and kobolds" model that the prior AL modules overused, and there are reasonable opportunities to avoid or mitigate combats through diplomacy or stealth for players who prefer that route.
It's not without flaws, though. The antagonist's plan doesn't really make any sense and is full of red herrings that confuse rather than entertain. The investigation phase is prone to being trivially skipped by smart players, or leaving players with no idea what to do next if they miss a vital clue. And the final combat features a solo monster with lair actions that (as printed) could conceivably kill an entire level-appropriate party before they even act. Still, DM intervention required to solve or mitigate these problems is minimal.
Also relevant - as printed, this adventure does NOT fit into the standard AL four-hour timeslot. The combats alone will take most of that time if you run them all, and the investigation phase is meaty and full of temptations to lengthy interrogation and extensive roleplaying. That's great if you have the time and the player interest - more content is also nice - but relevant to people who hope to field this at a convention setting or on a tight schedule.
Lastly, this adventure is set more firmly within the Tyranny of Dragons AL season than some others. Some existing investment in Phlan or the operations of the Cult of the Dragon is needed to get the most out of the story, and the plot threads here about the Cult's master plan don't get any closure within this module. That's not a fault - the module's intended as part of a season - but makes it perhaps not ideal as a one-shot or for slotting into an existing, different, campaign.