I thought your trivia-filled brain
Not sure if that's a compliment or an insult...
would pick that sort of things up automatically. Semi-realistic sci-fi shooter in which you use the environment to your advantage. That's the baseline and the similarities rack up from there.
Well, you'll have to lay on a lot of similarities, because I think that's stretching it.
Dead Space and Half-Life 2 are both sci-fi, but are very different. HL2 takes place entirely on Earth in the 21st century, and if it fits a genre, is arguably post-apocalyptic. Dead Space takes place in the 26th century, takes place entirely in space (or on an alien planet at the end), and is sci-fi horror.
As for the environment to your advantage...I guess? Maybe? But the experience of using the gravity gun and kinesis modules are pretty different IMO, not to mention that Dead Space's physics aren't as dynamic, while on the other hand, you can use the modules for a lot more.
I'll buy that Dead Space has influences from stuff like RE4, Alien, and System Shock, but Half-Life? Disagree, I'm afraid.