"It's best described as a rogue-like space game."
FTL is best described as "a totally random mess". I remember a roguelike where you had something like a 1 in 100000 chance to die instantly every time you went down a level. Up that chance to 1 in 50 and you have FTL. Don't waste a penny on it.
The Binding of Isaac, on the other hand, is well worth its tiny price. It can also be infuriating sometimes when you hit a bad run for items or get some nasty room layouts, but the RNG factor is at least held to a reasonable level.