One thing that I really liked here was how it was a suit that turns Griffin invisible, as opposed to a serum or something else that would have resulted in him running around naked the whole time. They also did a very good job of making you unsure of when he's in the room and when he isn't. I do think that Oliver Jackson-Cohen was a little wasted here... I understand making Griffin (literally and figuratively) the unseen threat, but pretty much everything we learn about him is from dialogue from other characters. I understand that they wanted to decentralize him but I felt like we could have seen the actor a bit more (maybe just at the beginning or at the end) because OJC is very good and he could have been utilized a bit better. I think back to Hollow Man, which was terrible, but one thing that did work was Kevin Bacon's compelling villain. I actually wanted him to win because I hated all the hero characters (Elizabeth Shue and Josh Brolin, phoning it in for a paycheck) so much, haha. But maybe that was the point here; they didn't want audiences to root for the bad guy at all. Though I don't know that anyone sane really would have even if they fleshed him out a bit more.
There are also a few plot holes/illogical things that happen. I'm not sure how exactly the faked Griffin's death; that seems like they would need more than just him and his brother in on the whole thing. Also, in the age of business email compromise, I can't believe that Cecilia's sister would have just written her sister off after receiving ONE nasty email, especially after Cecilia swore that she never sent it. These are nitpicks though. The movie overall is very effective and there were scenes that straight up SHOCKED me, which doesn't happen a lot with horror films, honestly. The scene where Griffin cuts the sister's throat left my jaw on the floor.
One last thing. A while back, when the rights to the Fantastic Four reverted back to Marvel, I was fancasting and I thought Elizabeth Moss might make a really compelling Invisible Woman. Looks like that might happen if they make a sequel to this, haha!