Castell's greatest asset are it's light ruleset and deep gameplay. Unfortunately, three of it's four main actions are not particularly engaging which leads to the bulk of the experience feeling bone dry.
The game state provides a wealth of information. I enjoy having a plethora of variables to account for, but Castell's approach to presenting it's mechanics is a huge issue. It's frustratingly difficult to intuit what your options actually are. To plan where you want to train for the next round for example, you have to visualize/imagine the wheel being turned once. Those will be the values you have to work with. Then you look for the region that your in/will be in. Somehow even spotting your region on the wheel is more difficult than it should be. The colours on the board and wheel are slightly off from each other. I found it more consistent to matching the region names on the board with what's on the wheel. Once you've matched the region your in on the board with the wheel, take note of it's associated training option. Now do this for all adjacent regions you have potential to go to. Your ready to plan out the rest of your turn, but don't forget which training options correspond to which regions or else you'll have to do it all again. All this information leads towards preparing for completing local performances and doing well at tournaments. There is a lot to opaque information to digest and because of that, turns can be long.
The branching training system also adds in the difficultly of evaluating what your opponents can potentially build and what their motivations may be. This means, other players will often swoop into your territory, rebuild their castell, and claim an objective you were working toward. That is a good chunk of the player interaction and it feels like having the the rug pulled out from under you.
Overall I highly value design that can squeeze a lot of strategy out of a small ruleset. The big issue here is that the game does not convey that information intuitively. Sacrificed is the ability to see what your opponent can accomplish. As a result the little player interaction there is, often feels blindsiding. The lack of intuitive information also means seeing the correct variables to make a well informed decision is convoluted and takes an annoyingly long time. In a game with actions as dry and paralysis inducing as Castell, the game feels more like work than fun.