Roguelikes must feel like chemistry sets to designers - they must feel like the cool ones you got as a kid which allowed you a limited creative licence to meddle, to blow things up, to set things on fire. I suspect that this kind of playful tinkering is where 99 Levels to Hell was born, with the developer taking an existing roguelike design template as a starting point - specifically Spelunky's brilliant twist on the roguelike as platformer - before tweaking, rearranging and then standing back to see what happened.
That's not to say 99 Levels is a clone. Spelunky's Derek Yu was working with established ideas in the first place, and ZaxisGames' dungeon-crawler brings a handful of additional concepts to bear. The main shift in focus is that - like The Binding of Isaac - 99 Levels is a shooter from the off, and one in which you're wise to keep your finger firmly clamped on the trigger throughout. Played with a decent pad, which is the way I suggest you approach things, the game is a fairly decent blaster, actually: enemies swarm in from all angles, crowds of foes require constant management, and you have to keep your reticule spinning around you in order to fend them off when things get really bad.
A sharper focus on shooting's not the only twist. The exit to each individual level now requires a key before you can pass through it, which means you've basically got two main objectives when spawning in a new stage instead of just one. That exit - and the entrance, in fact - can be located anywhere, too, meaning you're going to have to hunt high as well as low as you play. With no rope system in place, you can expect to get into a right pickle now and then, particularly when you're encountering levels filled with dirt that can collapse beneath you - but while the design employs a certain degree of randomisation each time you restart the game, the roll of the dice is largely focused on item placement and will never chuck you into a level that can't be completed.