Ultimately disappointing Annihilation is written and directed by Alex Garland who made a movie I loved, Ex Machina. Ex Machina has smart visual effects and the budget doesn't get in the way of the premise. It's a perfect match. It also has a good performance by Vikander. Obviously it gave me some expectations for this movie, but I think I can give it a fair review.
First let's start with the good, I think Portman is convincing, so are a few of the other actors in her crew. The story is in broad terms an expedition checking out an anamoly in a forest, it's interesting and it's rooted in science. There are some nice visuals and overall I would say the movie makes you think a bit like Ex Machina. But it's maybe more of an "experience" in a way it approaches thinking compared to Ex Machina.
In my opinion there are nice details to look at in this movie and the standard of effects are ok, but the visuals are cheesy, and look like overdone HDR photographs or games in many parts. The details of some of the plot is pretty bad, including a former soldier thinking a guard post on the ground as a good idea when they have a tall inaccessible guard tower to sit guard in. We know it needs to be "scary" and you need to set up events, but that is just so bad I won't even consider it a spoiler.
I think the bigger scope of the movie, with the bigger set and the bigger set of characters is it's biggest problem. It honestly feels like a B movie you'll see in the middle of the night in your countries 5th most popular TV channel for large parts of the movie. I think the smaller scope of Ex Machina maybe concealed some of the weaknesses and maybe inexperience of the director/writer.
In the end I would still recommend giving it a view, but my ultimate verdict is that it's a movie that would have needed a few more rounds in writing and planning. I honestly don't think it would have ended up on Netflix for the rest of the world if it did.