I am not a pro gamer. I think I may have played DotA once or twice, but if I did I don’t remember it clearly enough to distinguish it from other tower defense games. I did play Warcraft III on PC wayyyy back in the early aughts, and I liked that game for the story and the RPG-like, level-uppable heroes rather than the strategy per se, and was not at all interested in multiplayer competition. (I always get schooled in online multiplayer games, regardless of the genre.) I also especially liked the cartoonish “horror”-y elements of that game (if you haven’t played it, you spend a lot of time fighting the undead, and later becoming the undead) and its MMO offspring, World of Warcraft.
Hero Defense: Haunted Island is a tower defense game that employs a similar cartoonishly horror aesthetic. You play as a group of five heroes, and instead of building and upgrading stationary towers, as is the norm in these games, you move your heroes around the map and upgrade their powers as you go. Like other TD’s, there are several lanes down which enemies move, and your job is to kill them all before they reach a certain point on the map. Enemies don’t attack, they just advance on the map’s endpoint. It’s all very straightforward, with a simple skill tree for each character, and weapons you can upgrade by inserting magical runes which are activated during battle. The character leveling system isn’t very deep, but it’s satisfying enough. Like most of these games I’ve played, you can replay maps on higher difficulty levels and complete challenges to earn more money and experience. Your homebase is the town, which features several buildings where you can train heroes and spend your resources on further upgrades.

I’d live there.
The characters are kind of fun, generic horror tropes (I assume deliberately so). You have Jack the vampire hunter; Barrows the priest/gravedigger (because a barrow is a grave, get it?); Sam Hain (har har) the annoying fire witch; Jane Doe (again, har har) the reanimated corpse (kind of a Frankenstein shout-out); and Wylde Halfblood, the, er, half-werewolf? The names and background stories are all ridiculous and basically inconsequential, since the story is nearly nonexistent, and the tongue-in-cheekness of it all makes it amusing enough.
There are some gripes. On the broadest level, Hero Defense just feels like a glorified mobile game. The only appreciable difference is that you pay full price up front ($12.74 on Steam as of this writing) rather than pissing it away on in-game microtransactions. Otherwise, though, it’s almost interchangeable with about a zillion similar games you can download for free from Google Play. Sure, you have the heroes instead of towers, but in practice that’s a negligible difference (and other TD games also have heroes).
In terms of gameplay itself, it’s pretty smooth. The only issue is that, as far as I can tell, you can’t change the zoom level on missions, which doesn’t really affect play but effectively means you’re always watching tiny figures running around below as if from a distant hilltop.
There’s one thing I can’t let it off the hook for: Hero Defense has some of the most teeth-grindingly awful voice acting in recent gaming. The main character, Jack, speaks like a monotone android version of Casey Kasem. Sam Hain’s voice makes me want to rip out my own eardrums, and Jane Doe can’t pronounce the word “amalgam” to save her life. It’s all unfortunately just bad, not the B-movie so-bad-it’s-good kind of bad. (On how to actually pull that off, see Arthur from Fire Emblem.)

It’s like a robot impersonating another robot impersonating a human… impersonating a robot. (Happy Tuesday)
Those issues aside, Hero Defense: Haunted Island is pretty fun. If you want a deep game with strong RPG progression, customizable heroes, or a coherent story, look elsewhere; but if you want some silly, Universal movie monster-inspired horror fun, this is a good bet. And it has some theremin in the soundtrack. Points for effort.
I’ve never tried one of these games, but this sounds interesting enough. I like paying for a game completely upfront.
Is the learning curve steep? I used to play RPGs for the Nintendo and Commodore through the 80s and early 90s. Haven’t played many mobile games. Not really into multiplayer stuff.
It’s pretty easy to learn, and has a tutorial that teaches you the basics. You can technically play the game with just the mouse, but you’ll probably want to use the number keys to select heroes–much faster.