You get a ton of different spells (and another page of abilities) to choose from as you go, so it's very much a case of choosing your own build rather than being pigeonholed by RNG.
The variety and number of spell choices available seems to grow as you continue through the game.
When you clear a level, you get to choose between a series of options for the next one. You can even look at them before choosing it.
You don't confirm your choice until you actually choose where to spawn in the level.
I don't wanna spoil too much — I could post sooo very many of these — but some of the spells available are really dope.
I guess it's technically what you'd call a coffee-break roguelike, but it has plelnty of challenge in it. Oh, and it has great controls for keyboard and mouse.
Lots of flexibility.