Like most officially licensed game adaptations, Attack on Titan Tactics relies heavily on its leveraged IP. A licensed game like Tactics lives and dies off of its authenticity to the original. Luckily, DeNA and Crunchyroll Games are also partnered with Kodansha and Funimation who publish the manga and anime respectively. The game also features the original Japanese voice cast, plus the anime's opening themes. So it's got a good sense of authenticity.
However, rather than trying to make an Attack on Titan RPG like Koei Tecmo's Attack on Titan 2: Final Battle, DeNA and Crunchyroll Games have created a tower-defense RTS. Which, honestly, makes a whole lot of sense considering the first season of the anime, which is mostly about defending humanity's walls from the imposing Titan threat.
And considering Attack on Titan Tactics has launched with content for the anime's first season, that works out perfectly.
Attack on Titan Tactics comprises of several game modes: story mode, character episodes, and time limited events. Story mode, naturally, follows the story of the anime through cutscenes and various missions where players take on waves of titans. Character episodes are short, character focused side-stories that fold neatly into the anime's narrative for some extra information. The events include special events plus daily training, awakening, and money quests which help players strengthen their units.
The general gameplay for Tactics is comprised of story-mode missions that pit the player and their team of scouts against waves of attacking titans. Those titans come in various sub-types which each have their own strengths and weaknesses. There are also a number of Boss titans who are far more powerful and will require more effort to take down. The player defends their base by utilizing various character units, which all have their own strengths, weaknesses, and uses. Some units stay on the field for a long amount of time, working as your primary frontline fighters, while others target specific body parts or stay around long enough to execute a single titan before leaving the field.
While each type of unit has its uses, each individual character also has their own strengths, weaknesses, and limit breaks. So you need to know your squad well, and have a few different squads ready for different battles. After all, you might need to load up on quick eliminations for some fights, while others will require strategic use of limb-targeting units. Which makes it a surprisingly tricky RTS.
Attack on Titan Tactics' story cutscenes and character episodes are rather brief, which works best for a mobile game, as players won't always have time to sit down for a short movie. While the brevity of the scenes does make it easier for players familiar with the anime, those who haven't watched or read Attack on Titan can easily pick up the information that they need.
As for the in-app purchases, most of the things a Tactics player will need can be picked up for free using the crystals they earn by completing objectives, logging on daily, and completing the story missions. So you can definitely play for free. There's a bit of a stamina counter, but it's really only used during the special events and daily training events. So you can play through the story as fast as you like, assuming your units are leveled up enough.
All around, it's a solid mobile game. The biggest problem I have with Tactics is its 3D character sprites, which look a bit too N64 for my personal taste. The UI is also servicable, if a little bit clunky. Which is a relatively minor gripe considering this is a mobile title.