+ Amazing characters
+ Fantastic soundtrack
+ Simple, but interesting story
+ Despite having many visual effects, the game is very easy on the eyes
+ Not hard enough to be stressful, but enough to provide challenge
+ Dailies and leaderbords for competitive audience
+ Co-op
+ Pretty wings

- Some things may feel unfairly hard (comes with the genre, I guess)
- Rather short story
- Not too much weapon variety aside from every android having 2 different types of attack
- Only 3 power-ups (speed boost, time freeze, turrets), which again is a lack of variety

I don't know where to start with this game, so I will start with the most important thing. Assault Android Cactus is undoubtedly one of my favorite games ever made, and I don't say this lightly. It's weird to say, but I don't really compare this game to other twin-stick shooters. I compare it to Devil May Cry 3. Because this is exactly how it feels to me (except, it has better controls).
It is action sequence after action sequence with witty commentaries of loveable characters who go through a cheesy, yet interesting story, while listening to absolutely fantastic music. All of this makes you forget your troubles and ultimately, I think this is what games are for.

I'm not a huge fan of twin-stick shooters or bullet hell games. To be honest, I'm just bad at them. They are so bright, everything always explodes and shoots at you from all directions, I just get lost, don't know if I should watch my aim or my character, it's all very overwhelming. And sure, there's that element in Cactus as well, after all, there are tons of enemies and bullets and it is a fast-paced game. But it feels more structured. I rarely feel lost, the difficulty curve is very nice, so you have some time to get used to things before they kill you brutally AND when they do, there's still chance for recovery.
I would say that in regards of difficulty, Cactus is on a more casual side of the genre, but that's not to say it's easy. It's just a little more forgiving. Casual players like me will find sufficient challenge while moving through the story, whereas more hardcore fans of the genre will find themselves fighting against timer and trying to maintain combo meter to get the highest scores possible (which is lost upon death, unlike the level progress).

The explosions, bullets, lasers, fire, spikes, environment destruction etc., etc., are so nicely tuned that you never think "oh god, please, spare my eyes!". It's all greatly balanced, so you can see everything that's going against you clearly, enjoy the beautiful graphics this game has and not feel like your eyes have been violated after a couple hours of playing.

One of the reasons I generally can't get into bullet hell games, aside from difficulty, is lack of interesting story or characters. Which is not to say there aren't exceptions, but still, they are generally heavily gameplay focused, so the rest is secondary.
Cactus fixes this problem. Every character has unique personality, which is reflected in the story and dialogues (they all have unique encounters with bosses), and, which is even more impressive, in their animations - their victory poses, their selection screen when you pick a character or cancel selection, with some of them feeling scared, pumped-up or disappointed. And the unique commentaries a certain character provides are priceless (like, calling "speed up" boost "pretty wings" for example). I never expected to love characters in a game like this as much as I do. You can easily see that they weren't an afterthought, but are as much of a game's focus as the gameplay itself. And the aforementioned unique boss dialogues add replayability if you want to see every character's interractions.

And of course, one of the main reasons this game is such a blast in my opinion... the music. The soundtrack is phenomenal. I very rarely buy soundtracks for games. Or even pay attention to it. The only exceptions I can think of from the top of my head are Persona series, Crypt of the Necrodancer, Sentinels of the Multiverse and... well... Assault Android Cactus. That's it, I believe.
I'm not sure if the music dynamically changes during the level or it's just written so that it feels this way, but it always, and I do mean ALWAYS fits what you see on screen, becoming faster and more aggressive as the action intensifies. It helps you get into the rhythm of the action so well that sometimes it starts to feel that you are playing a rhythm game. This flow of the music during levels, along with the pumped-up feeling it fills you with are probably the most important reason why I love this game as much as I do.

That said, this game is not without its flaws... for once, it's one of the dumbest game names I've ever heard.
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Just kidding, it's awesome. Or rather, it is so stupid that it is amazing. If it wasn't for the name I may have overlooked the game entirely. But no, I just thought "WTF? What kind of name is "Assault Android Cactus"? I just NEED to click it and see what's up with it". And then after you play the game it actually makes sense and doesn't even sound stupid anymore.

But on a more serious note, I actually do feel like this game has at least one flaw. And it lies in its achievements. I can't say that I'm a kind of person that absolutely MUST get 100% achievements in every game he plays. But that's what I strive to do with the games I absolutely love. And, as you may have noticed, I do love Cactus.
So, what's the problem with the achievements? It's the requirement to get "S+" (which is the best rank possible) on all levels. And here's the thing, to get "S+", you must be perfect. Literally, perfect. Not dying, not losing your combo even once, basically not being hit. And between this requirement and me being mostly a casual player, it's just driving me insane. And don't get me wrong, striving to get better in a game you love is amazing. Getting an "S" rank is a joy for me. It usually happens when you have a blast with your favorite character and it's when the game is at it's best. Getting S+ is more of a... "Was it even worth it? I'm not even having fun anymore..." situation. At least for me.
And then there's luck factor, like, when you have that "S+" ready for the grab, and there's just one enemy left, and you just don't run to him in time because he's on the other end of the map... "fun" is not the word I'd choose for this situation.
But of course, achievements are such an insignificant thing that it's honestly just a minor complaint. And it is a reward for better players out there to grab. However, if you are a player who just NEEDS to have that 100% achievement in their game, get ready for quite a bit of pain.

So, to end this review, I want to once again mention one simple thing. When I was in college, Devil May Cry 3 with its endless mode used to be my go-to antidepressant. I knew that if I felt down or angry I could turn it on and just slash some demons, while slashing my troubles away with them. Now, Assault Android Cactus took that niche. Whenever I feel bad, this game with its colorful characters, action-packed gameplay and lively soundtrack is here to cheer me up.
And I truly hope that you give it a chance as well. It is absolutely worth it. Especially considering it's low price. Compared to the amount of emotions I personally got out of this game, it's just nothing.

Assault Android Cactus deserves far more recognition than it currently has.

It is hands down one of the best games I have ever played.