Annihilation wasn't as bad as Ad Astra (no connection, just another weird failed sci-fi movie from around the same time, which somebody happened to mention in these comments) but was a fail on many levels.

People talked about the amnesia cut when they first go in and their rations are gone, yeah I liked that moment except then I don't believe anything else in the movie ever re-used the same phenomenon of missing elapsed time. Because the movie is a jumbled mish-mash of inconsistent nonsense.

Everybody is talking about the bear, which indeed was scary, but seems like a writer coming up with a scary thing but now being able to connect it to anything in a relevant way. It's also an excuse for the (OF COURSE) gung ho firing of machine guns. Of course a movie superficially about some scientists going in to succeed where the pure military guys failed shows the characters all with M16's or whatever: American gun fetish. Gotta have guns. The only good angle with the gun stuff was that the science team got further than the soldier team. I actually like good soldier story stuff, and this is quite an affecting example where a team prepared in the exact wrong ways both physically and mentally for a mission are doomed...and not through a fault of their own necessarily, which makes it all the more tragic and disturbing.

Anyway the biggest fail of the movie was the shallow use of natural environments: the woods, the water, vegetation all around, and with the conceit of mutations and biological alterations (etc etc) yet no weird lifeforms were ever observed at all except for a couple cases of needing to shoot machine guns again (the bear, the crocodile). Any idiot who has ever been in the woods knows that you are SURROUNDED on all sides by bugs, mosquitos, birds, salamanders, small mammals, dragonflies, blackflies, moths, fish, moss, fungi, algae, and yet this movie ignorantly has no awareness of any of this except for a couple Capital S Scenes for guns (shooting a scary bear monster, shooting a crocodile). Now I know that may seem like a thin criticism, but keep in mind all the biological pretense of this movie (like a character suddenly becoming a plant, and everything else) and the fact that it takes place in a lush natural wild environment, and yet...almost zero critters.

The ending was also pretentious crap with the silly metallic dance-like alien doppelganger thing. The core idea here is good and scary, especially with how a neutral innocent movement inadvertently causes the opposite movement which then causes protagonist to get temporarily crushed (that's great writing for a psychological/biological/sci-fi/confusion scenario), but the way it was done visually and direction-wise was crap.

I do want to say that apart from the amnesia ellipsis (which I liked, when it happened), the giant worm portal thing in Oscar Isaac's abdomen was also another well-done disturbing sci-fi/psychological/body horror/anomaly moment.

As a point of contrast, when someone like Tarkovsky makes a movie like Solaris, I think he actually thinks more about his ideas and commits more, whereas Annihilation is an inconsistent mish-mash and compormised.