(I am porting over older reviews from my BGG profile. These might be old and/or bad. Please excuse their old-and-or-badness.)
Let’s get it over with: Obviously this game looks similar to Blokus.
Comparing it to that game is sort of pointless, though. Blokus BY DESIGN has a tendency to let players escape, and you have to put in a lot of work to successfully lock someone down. This game has the opposite rule, pieces must be connected by sides rather than corners, and as such has a very different feel, simultaneously more aggressive and more forgiving.
This game, despite the appearance, feels a lot more like enclosure/connection games like Twixt or Through The Desert than a space optimization game like Blokus. Because of the way pieces must be connected side to side, and the starting placement mechanic which keeps players out of the very center of the board, the early game is a race to enclose as much area as possible while simultaneously attempting to enclose your opponent, forcing them to burn their third column early. That third column is the centerpiece of the game, and provides the game’s defining moments of uncertainty and tension. Once each player has placed their column, the board is stable and players can optimize with the rest of their moves; Until the third column is placed, areas are never really ‘safe’ and players must gain access to as much potential area as possible so that when a player invades one previously ‘safe’ area they can either defend or simply expand in some other direction.
This description makes it seem that this game is highly aggressive… it is, but it is also highly forgiving (especially with newer players). For example, it is tempting to try to quickly enclose an enemy’s starting position and force them to spend their third column. In doing this, we are probably not enclosing a lot of space ourselves, and the enemy’s third column will be placed in a further area, giving them plenty of liberty / open space while we have expended many tiles to lock down their opening area. This hyper-aggressive tactic is attractive but can end up being a break-even proposition. In my experience it seems more valuable to make aggressive moves only when necessary, instead focusing more on enclosing and expanding one’s own territory, gobbling up optimal third-column spaces so the opponent cannot gain much from it.
I also like the zig-zag “diagonal” edges of the board. This makes plays for enclosing an area a bit stronger and easier, while also making pieces with long edges (great for reaching the sides of the board) harder to efficiently place once actually AT the side of the board. This simple change gives some pieces more value than they would have on a square board.
My main issue with the game is just that the move of the third column seems far more important than any other move in the game. The rest of the game is almost auto-pilot compared to the weight of the third column moves. Based on those placements, the momentum of the game can very suddenly shift. Other games of this type lack such singularly dramatic moments, but the issue of making other moves feel less significant in comparison is definitely something worth noting.
All in all, I would recommend Callisto to players who enjoy abstract games of an area enclosure or area connection nature, especially if found at a bargain price. There are other abstracts that I enjoy more, but I wouldn’t refuse to play this game, and it’s original enough that I definitely don’t fault it as a knockoff.