Truthfully, going into this game, I didn't know what to expect. With the name telling me I have 30 seconds to complete a mission, I thought it was going to be very easy. This is far from the case. As others have mentioned, this game makes you think strategically about when to grind, when to spend your money, how to spend said money, when the best time to fight the boss would be, etc. It's this balance while forcing you to think on your feet that makes it so interesting. Some missions you may beat the first time, others, especially the bonus missions, may take you two, or three, or even more attempts at them, but you will most likely end up loving it every time and, at least in my experience, rarely, if ever, ever give up in anger because it's that fun and addicting.
Would I say it's one of the best games I've ever played? eh, not really, but it's definitely up there high on the list. Reason for this is while yes, the game is fantastic and addicting, it's also really repetitive. This is probably it's biggest, and only flaw in my eyes of the game. Now don't get me wrong, each stage is set up to give you a new challenge to get to the boss, such as monsters are absent from the map so you can't level up, an avalanche can hit you causing you to lose all your armor and weapons, etc. but at it's core, it's the same thing each level. Grind early, reset time, buy items, grind a bit more, reset time, proceed to go through the stage, reset time, fight boss, go to next stage, repeat.
If the thought of repeating the same core gameplay every stage doesn't appeal to you then I'd recommend watching a few videos on youtube or watching other people play it on twitch or something first to see if it really isn't your thing. If you can look past this flaw then you will most likely enjoy this game and for ten dollars, it's not too bad of a price if you can afford it.