Quoted from PACMAN:The "you're playing AS Ripley" angle is still pretty weak.
Imagine these pinball machines with the main character replaced by the player.
T2 WITHOUT Arnold.
Nightmare on Elm Street WITHOUT Freddy.
Apollo 13 WITHOUT Tom Hanks.
The Avengers WITHOUT Hulk.
Tron Legacy WITHOUT Flynn.
Demolition Man WITHOUT Stallone.
Star Wars WITHOUT Luke.
Addams Family WITHOUT Gomez.
The Shadow WITHOUT Alec.
Kiss WITHOUT Gene.
TBL WITHOUT The Dude.
Iron Man WITHOUT Stark.
Jurassic Park WITHOUT T-Rex.
Batman WITHOUT Batman.
etc...
That being said. The Game is still really amazing in spite of its main, beloved character being absent.
I think the comparisons you are trying to make would be more akin to having an Alien pin with no Alien. Ripley is a main character, but the creature is the star. The game is just fine without her in it, and so far as the "play as her" angle, I think it fits very well. Just my .02 cents.