One of the reasons why Platypus isn't really as challenging as it first appears to be is the game's continue system. When you start a new game you'll have four additional lives and two credits in reserve. You'll earn extra lives as you progress, and at the end of each level you'll be awarded another credit. It's still tough to beat Platypus on a single play-through, but when you start a new game--complete with those same four lives and two credits--you can choose to start at the beginning of any of the levels that you've unlocked. The result is that you can beat the game without ever having completed more than one level in a session. This isn't necessarily a criticism, since it would certainly get frustrating if you were forced to play through the first level over and over again, but it might be a turn-off for those of you with masochistic tendencies who were hoping for some old-school coin-hungry-style arcade action.
In addition to the single-player "story" mode, which might take you around five hours to play through on your first attempt depending on your skill and the difficulty level, Platypus offers ad-hoc cooperative play and a survival mode. The cooperative mode lets you play through the entire story mode alongside a friend with whom you'll share a common reserve of extra lives and any power-ups that appear. If you die in a co-op game and there are no more lives for you you'll get to stay on the screen in a transparent craft and watch your friend continue playing, and if he or she manages to earn an extra life you'll be put right back into the game. The survival mode plays out much like the regular game, with the caveat that you only get a single life with which to take on the enemy. This is a great mode to play if you don't have a lot of time because, although the default top score for it is certainly beatable, the fact that it's set to only two minutes speaks volumes about just how challenging it is.
It's the sheer number of enemies rather than the enemies themselves that make the game challenging.
While Platypus' visuals are repetitive and don't always look a lot like Claymation, the game's audio is rather impressive. The sound effects for weapon fire and explosions aren't up too much, but the list of composers involved with the soundtrack reads like a who's who from the Commodore 64 era. Rob Hubbard, Martin Galway, Matt Gray, and Paul Norman have all had a hand in the soundtrack, which includes remixes of some of their more memorable works from such classic games as Wizball, Parallax, Sanxion, and Driller. There are only eight music tracks in total, but there's not a weak one among them, and given that they're all taken from quite different games they work surprisingly well together.
Platypus is fun while it lasts, and there's certainly no shortage of challenge if you opt for its hardest difficulty setting. For the asking price the game is very bare-bones, though, and the only incentive to play through the game again once you're done is to try for a higher score. There's nothing horribly wrong with Platypus, then, provided you can accept it for what it is--an unambitious, simplistic, and short-lived shoot-'em-up.