I beat it in 2:38. I wouldn't have minded a briefing, even if just a "In Game Briefing: Press Start" or something. I also think you could do a little bit more with the boss. Like, make him always attack Malvanis, that way he chases you more consistently. I wouldn't say it was too easy, but I would say that it's not a very compelling introduction to a longer campaign. I wouldn't mind having some idea of what it's about, who this character is, etc.

You can't win the game without that extra marine. To win against the three marines at the end you need a little bit of micro, Done wrong, you die quickly.

As well as being short, its abit too easy. The shorter it is, the harder it should be.
Also,: Did you get lazy? You're forced to enter the last room with that extra marine with you. Not one by one