That's twice in the last 24 hours you've used the 'it's a game' argument. So, because it's a game means we should lower our expectations and accept mediocrity as the norm?
It is entirely possible for characters to appear too often and to not have enough screentime. In this instance you have a character who frequently pops up but has little time to create any resonance. Sure, it's his significant other, but we (the player) are not Isaac, we only control him. A minute in Nicole's company might bring back a flood of memories for him, but I might only know him as the dude with a gnarly mask who strawberry floats up hellbeasts or whatever. The whole thing plays out in realtime, which is its biggest flaw. You can effectively use montage and flashbacks to detail the emotional connection, cover years worth of memories in what is figuratively a few seconds, but instead it leaps from one scene to the next, and there's no time to let his actions sink in. Everything is driven and exciting, and as a consequence I'm given no real time to empathise with Isaac as a character.
Maybe I should amend my comment about the voice acting. It's flat and emotionally vacant, the traits you'd associate with a low-rent student production.
If I could've articulated how I felt about dead space 2s narrative without using the word 'gooseberry fool', 'bollocks', and 'lose of gooseberry fool bollocks', it would've read just like what you wrote.
Also I have no idea how anyone could've found the end of ds1 emotionally affecting. Isaac sits down, takes off his helmet, and nicole jumps up behind him and goes BOO. Wow.