PixelJunk Monsters Ultimate is a tower defense game that requires constant attention from the player. You play as a Tiki guy defending a hut from waves of monsters. On the surface, it seems like a cheerful casual game... but looks can be deceiving. There are almost never any lulls in the action, so you always have to be on the move, planning ahead. Resources (used to build towers) come in the form of coins dropped from enemies. However, you actually have to run around and collect the coins yourself before they disappear. Similarly, in order to build towers, you actually have to walk to where you want them first. Towers can also be upgraded by standing on them, a process that takes time. Enemies also sometimes drop crystals, which can be spent to quickly upgrade towers, or saved up to purchase other types of towers. So gameplay boils down to a test of multitasking skills - you have to balance anticipating what towers need to be built (and where), while simultaneously collecting dropped resources and upgrading. It gets pretty intense.
Most levels can be completed easily enough in 1 or 2 tries, but the challenge comes in trying to do so perfectly (not letting even 1 enemy get to your hut). Perfect-scoring levels unlocks more levels to play, and so on. And that's where the challenge (and unfortunately, frustration) comes in. The main down-side to this game is that it can sometimes be very unfair. While there is an indicator that shows what types of enemies are coming up, it's not always clear enough (for example, a blinking red icon sometimes means "weak to cannons", and other times "on fire and 3 times as fast"). Also, sometimes enemies take completely different paths with no warning. These types of things are frankly just bad game design and complete BS. The best TD games allow you to deduce the path enemies will take and plan ahead accordingly. This game doesn't always do that, which leads to having to sometimes rely on memorization rather than actual skill. Thankfully, it doesn't happen a lot, but that doesn't make it any less frustrating when it does. That said, this is a small complaint when compared to how good the rest of the game is, but it is a noteworthy enough issue that it needed to be mentioned.
The main game consists of 47 levels, with an additional 24 challenge levels that can be unlocked. The challenges are levels that have to be cleared while also fulfilling some sort of special criteria (completing challenges unlocks concept art, videos, music and more). The game also has a 2-player co-op mode, which I haven't tried (but it seems like it would be really fun). All in all, between the main levels, challenges, and co-op, the amount of content available is pretty substantial. I've sunk around 60 hours in already (though technically, most of that was spent replaying levels over and over again trying to get perfect clears), but still, the fact that I put that much time into it speaks to how good the core gameplay is. Despite my rant above on the few down-sides that sometimes make it frustrating, overall, the game is solid, and lots of fun to play. If you like tower defense, this is a great one. The price seems a bit high, especially when the original version on PS3 was cheaper, but there is also more content in this version compared to the original release, plus the added multiplayer component... so I suppose it is probably justified. If you are into TD games, definitely pick it up in a sale at some point, if not at full price.