Its a good layout and implementation of an idea...
Some criticism, hopefully constructive.
The merging process is awful. If you can ONLY merge identically leveled dice, why allow to select both dice? Either make it so you can merge different dice with some element of random change of sharing upgrades (could result in stupidly powerful dice perhaps? Maybe an expansion of the current game play? OR only be able to select from dice you have an even number of and allow the player to just select one level of dice and upgrade from there? In its current form the dice re-order themselves which makes clicking a chore.
I've merged countless dice so far and the game is almost going to get nicknamed carpel tunnel game. The majority of the game play is spent moving the mouse back and forth between the dice square and the dice you want to merge. If you can fix that to some degree you may appeal to more players, especially those who may have carpel tunnel already.
Haha very nice feecback! And you even made me laugh in the process! We'll sure take that into consideration another time! I'm glad you took your time to talk about the issue about moving the mouse a lot to merge dice. We might want to take a step back and brainstorm ideas on how to solve certain design problems before rushing ahead and create the first idea that we come up with.
Thanks for playing :)