Intense shooter, but can't say it is too much of a challenge. It's rather easy.
For those seeking the "Wasp" (speedrun) the most valuable tip I can tell you is, after you get the SMG, shelve your pistol. SMG gets lots of rounds and outclasses pistol in DPS. Use every other weapon, don't spare any ammo (don't waste either). The second tip is to rush exits (as soon as they are open) and, at the final battle, shoot only at the boss. Also, don't die, you'll get the Spider for that.
I still used the pistol sparingly on my run, and got a 9:33 time, so it's not even that hard.
For the crocodile and crawler run, just do the exact opposite: Use pistol a lot and only leave a room after searching it entirely (some enemies spawn after the door is opened). DON'T COLLECT THE RIFLES AT ALL, JUST IGNORE THEM (you can collect their ammo without penalties).
No more than 2 runs (wasp+spider, and crawler+crocodile) are needed to achieve the final medal, but it may be wise to do a full run first to learn about the game.