Hello, game!
Here is a Tower Defense game that is worth playing, absolutely so if you're into Tower Defense and a good try if you are not that much into Tower Defense.
(I recommend you try the first one though, "Cursed Treasure: Don't Touch My Gems!")

Just like all games, it has goods and bads, unlike the other reviews, I'll make a list but don't take it as something simple.
I will start with what's bad, I like what's bad more than what's good, at least to talk about.

CONS:
- Story
The story in this game is rather weird. On the first three levels, it seems to have a good and proper story; Villagers are being send to mass-tower-slaughters just to desperately get some gems, these gems a giant queen wants on her fingers.
But after that, it all gets from "Defend your gems" to just plain "Let's conquer lands--and oh, don't forget the gems, we defend them...Don't even know why".
A sharp turn from the story. I'm not much into stories for Tower Defense myself, but I can understand if somebody would really hate this to happen. Well, if you are really into stories, I'm sorry but you must expect a very bad one.

- Graphical Diversity
The graphical diversity is rather bad, just like in the first but not so much.
You do get different tower aspects, different levels, different enemies (Especially after level 15) and so on.
BUT the land/terrain is nearly always the same. Take Level 4 as an example, it is set in some frosty mountains, but you don't really see so much frost.
Worse yet, all enemies just have the same 'face' (eyes), they're big and oggly.
If you reach level 10, you'll face the Wizard, who actually looks a lot more like a Scientist, they gave him a very bad aspect sadly enough.

All is not bad though.
The bad diversity will go away when you get to level 16 and up, you'll meet new (and way harder) enemies that differ too much from the other levels.
And yes, you will see 'clones' of many different enemies but this is done for practical reasons; It's hard to see a different enemy from another unless they have obvious differences, this is why most enemies have obvious features compared to many other units, while not being exactly diverse.

- Sound Diversity
Yep, this issue also appears in the original/first game as well, that is "Cursed Treasure: Don't Touch My Gems!" if you forgot.
Sound Diversity in Cursed Treasure 2 is actually better than in the first, but not so much.
For example, the female enemies have their own feminine voice, meanwhile ALL the other creatures just have the same male voice, even the bosses and even those of other lands (level 16).
It gets annoying to hear the same voice again and again.
The music doesn't offer much in diversity either, there's pretty much only 3 and they appear in all stages.

PROS:
- Diverse Upgrades
If you take a look, there's plenty of upgrades and all require more than 5 points to fully upgrade them. That's fine though.
Sure, most of them look very boring, some are boring-but-practical and some are situational, but the thing is, most of them ARE very useful.
Without mentioning the 5th skill on top, which is simply to reduce upgrade costs, the rest are very useful indeed.
Best example I can give is the 4th skill on top, for the Undead. It's only a 1% chance to insta-kill somebody, but guess what? It may not work on bosses, but it works on CHAMPIONS.
So if Lady Luck french-kisses you this day, boy will you be pleased. (For the insta-kill, not the french-kiss, it's a bonus though!)

Not just that, the "Mine" upgrades and the "Passive Effect" upgrades are all but worth it too, making them a lot more practical and more fun!

- Rank System
So. most Tower Defense games have an upgrade system, global or ingame. Most of these TD games also use these upgrade systems to be star-based, so you beat one level perfectly you get all stars and can use those to upgrade something, but you can't get more stars from that level.
Cursed Treasure 2 uses an XP system instead, based on 'Ranks'. This means that you can virtually play/farm and level and get as much XP as you can in those levels, no need to perfect-play a level (although it is recommended for more XP).
Best part yet, you can pretty much downgrade your upgrades to upgrade another, reset your whole upgrades too. Lately this practice has been seen in many new TD games, so it's not really something new, but it's worth to know, you wouldn't like to play a TD game where resets are final no matter what (Unless the system done for such is perfectly done so).
Also, if you wonder if you can unlock all the upgrades, you can! But it will take a long while, you have to grind for them.

- Worthy Achievements
NOTE: This isn't related to badges or Armor Games achievements, it's about the IN-GAME Achievements.
Why are they worthy now? Simply because they give you a reward if you get them. I hate achievements myself, they're just idiotic tokens that mean nothing but shitty brag.
But in Cursed Treasure 2, if you get an achievement you get extra XP and that is always useful!
So don't be shy now, get those achievements, they are worth it!

OVERALL
This is indeed a game way worth playing. As I said before, especially so if you're into Tower Defense. You'll surely love it, with guarantees.
Just be wary that if you hate Tower Defense...Well why are you even playing this?
Even if you're not that much into Tower Defense, the game is still worth to try it.