Not a bad game by any means, though there are a lot of caveats to that.
So first off, League TD is extremely oldschool style tower defence. Like we're talking Starcraft 1 era maps or earlier, not even Warcraft III era. It's good for what it is in that regard, and if you like those old tower defence style games, it's totally fine for what it is.
So what do I mean by that?
Well, all the towers more or less work the same way with very, very few exceptions. Almost all of them are just "shoots at a target" style. Meaning things like poison towers are kind of awful because they'll just shoot a single target over and over, making them pretty bad. There's also the whole status effect immunity thing that a lot of old games had, so of course enemies can be immune to ice (freeze in spot), lightning (slow movement), and poison (damage over time) which further makes these towers not that useful, and after about halfway through the game, every level you go to will have some of each.
There's also of course the flying enemies that are immune to everything but a single tower type and only if you upgrade that tower type with a specific optional upgrade for each individual tower. And invisible enemies that can be detected one at a time by a specific tower type with a specific optional upgrade again as well.
There are no buildings you can place on the track itself, so no mazing, no "enemies have this effect when you walk over it" (except one optional upgrade which can draw a weak damage straight line across a lane), and basically just assume that you're looking at the absolutely earliest days of tower defense games in terms of conceptual mechanics.
Now, with that in mind, the towers can be upgraded quite a few times, with each individual tower getting to choose optional upgrades at specific levels, basically as follows:
Level 3: Pick one of 3 stat increases
Level 5: Pick one of 2 special abilities
Level 8: Pick one of 3 with 1 and 2 being upgrades to the level 5 version, 3 being the core tower
Level 10: Pick one of 2 weird things
The thing is, most of these upgrade options do almost nothing. They do let you customize each individual tower, but the customizations aren't that important other than the ability to attack air and invisible enemies. Things like "do the equivalent of 1 attack's worth of damage as AoE every 5 seconds, but you attack 10 times per second so it's not actually noticeable."
There's a large tech tree... sort of. Except absolutely everything on the tech tree is locked behind needing to progress past certain levels, and the resources you acquire are rather limited in how they're handed out so the choice is largely an illusion rather than a real choice. It didn't really need to be a tech tree, and there's not much need to grind for resources hardly ever because most of the towers aren't actually useful at all (poison tower for a really obvious example again due to how the game mechanics work), unless you explicitly forgot to purchase the ability to upgrade your new "can shoot air units" tower so it can actually, yanno, shoot air... and spent all your resources and are now stuck on a level with air. Fortunately you can just play any given level as many times as you want and it still gives full resource drops each time.
The game has a looooot of levels... 50 of them, in fact. They probably honestly only needed 20, because it mostly drags on after about halfway through where you're not really getting anything particularly new to do and the enemies are more or less the same from that point onward. They keep gradually adding new enemies, but they don't really do anything particularly meaningful. Yes, they have new status effects they can put on your towers, or can put up a shield on themselves, but it doesn't actually change your build any so it's kind of meaningless. It's just longer levels with enemies that have more HP and you get more starting money to spend on more towers. That's about it. If you like that, which you probably do if you're playing this kind of super oldschool tower defense game, then yay, you should be happy with this as it's just an excuse to do more of the same.
The graphics are fine, nothing too special, but it does look nice to see your towers actually being modified with extra guns slapped onto them, the upgrades actually visibly shown and so on. Each group of 10 levels has a different set of new enemies and a different background, each individual level within the group of 10 is a different layout with some unique appearance to it, but it's a tower defense so you're probably not really concerned about eye candy. The attacks are fairly generic, but the sound effects are fairly well done, and fast firing towers actually fire fast which I appreciate.
There are a few issues to consider though other than gameplay.
First, it's a Chinese game. It wasn't fully translated, and there's some pretty notable issues with Engrish here and there. Usually it's fairly clear what they're trying to say, but sometimes it's really not obvious at all. Many of the tooltips, even when set to English, will still be half in Chinese.
The tooltips themselves are also often not very helpful. Not just as translation errors, but because they don't actually cover the information you want to know in the first place. LIke it'll tell you an upgrade increases the range of a tower, but often it won't tell you by how much. You have no idea what the base range or damage of any tower is either, so it's pure guesswork on whether an upgrade is actually worth it or if you'd be better spending your resources or money on something else. This is again, fairly oldschool in setup, so you may be used to this concept already.
There are a number of typos and bugs, such as tower tooltips which were clearly copy/pasted over from another tower and never re-written, or one situation where a tower upgrade to give it anti-air failed to actually attack air units. That was the only gameplay bug I saw though, and it only happened the one time, so it's "mostly" bug-free in any meaningful way, but there will be a ton of little, obvious errors all over the place.
There's also the fact that it's a Chinese game, so... they steal stuff. There are direct references to the Zerg, for example. You just kinda expect that from a Chinese game though, they're not really that big on intellectual property laws over there, but if stealing stuff is a deal breaker for you, you should be aware of it.
Otherwise... it's not a bad game. It does absolutely nothing groundbreaking or new. It doesn't even try to do anything new, and suffers from all the problems Tower Defense games circa 2002 had, when WC3 was just new and people were just learning what you could do with them but not what was a good idea to do yet. If this is what you want, it really does have that oldschool TD feel to it, but it doesn't really have anything for modern nicities other than the graphics. It's worth the full $5 CAD that they're asking for I'd say, it's fine even when it's not on sale.
Just, as stated, it will feel OLD. It will feel unpolished, unfinished, but it's not actually legitimately broken in any way.
The closest thing to broken it comes in, is it starts off in Chinese text to begin with, and if you don't read Chinese, then you'll have to guess at each menu option until you see one which has a menu option with a British flag you can click on for changing things (about 3/4, anyway) over to English.
Overall it's fairly solid, if simple, and while it doesn't do anything particularly new, nor does it do anything with any sort of grace or elegance, it does it fairly competently. It's not a bad tower defense game at all, but go in understanding it really wants to be from the first wave of early WC3 TDs, or the last wave of SC1 TDs, and it really isn't going to deviate from that throughout the entire experience. It's about the most generic "oldschool style TD" that you will ever see, but it does that well.
