Once I got my little equipment issue out of the way, Hero Siege proved to be a fun, but mindless twin-stick shooter. I wound up beating the game after a couple more hours, and then spent the rest of my time grinding my character up to maximum level.
I enjoyed it, but I wouldn't necessarily call it "good." The game has basically no plot (there are monsters attacking people, I guess) and while the randomly generated levels have a decent variety to them, none were particularly memorable. But compounding the game's basic blandness is the fact that once you play through on normal difficulty, you need only repeat the pre-boss levels on the higher difficulties.
But you know what, it's all right. Throwing hundreds of fireballs at massive hordes of enemies is oddly relaxing, once you get to the point where you don't have to worry about dying. Even if I didn't understand the late-game mechanics (like, what the intended level range for "hell" versus "inferno" is supposed to be, or why every damned piece of Legendary or Mythic equipment had a level 150 minimum, or literally anything about how the wormholes work), I still got the satisfaction of seeing numbers going up, and that's all that I really care about.
Overall, I'd say that Hero Siege is a game I would gladly play again, and mostly that is thanks to the strengths of its genre - a loot-driven action-rpg with complex character customization is the sort of game I've played many times before and will doubtlessly play many times again. It has its unique quirks, namely a fast-paced twin-stick shooter style and a class list with a couple of eccentric additions like "pirate" and "redneck," but I'm not sure those quirks are a specific draw. It is the variable schedule of rewards combined with a steady sense of forward progress that really makes games like this appealing.
Still, I got through it in just three days, which is amazing for a game that I was convinced I was going to hate. So let that be a lesson to anyone reading this - don't let your misconceptions hold you back, especially if those misconceptions are based on you being a huge idiot and missing, like, one-third of whatever it is you're judging. Maybe it's narrow advice, and maybe it's only useful in retrospect, but that's what I'm taking away from this experience.