The first modern rug I bought was a geometric gray and white thing from a shop that also sold inflatable furniture, back when I was renovating a little single house on the peninsula and needed something fast for a client's den. It taught me that a bold pattern on a cheap backing will curl at the corners within a year and never lie flat again, no matter how many books you stack on it.
A good modern rug sits well in a room that already has some age to it, oddly enough. Heart pine floors, a plaster wall with a little texture, an old chest of drawers you inherited or found at the salvage yard, all of that gives a clean geometric rug something to push against, and the room ends up looking collected rather than showroomed. It also does fine work under a plain sofa in a rental living room, or in a kid's playroom where you want color without a cartoon character on it. Where it struggles is in a room that's already busy, a lot of pattern on the curtains, a patterned tile floor peeking out from the kitchen, a gallery wall with twelve different frame styles. Put a loud modern rug in there and the room starts arguing with itself, and nobody wins that argument, least of all you, standing in the doorway wondering why it all feels like too much.
What separates the ones worth owning from the ones that end up rolled up in a closet is almost always in the back and the edges, not the front. Flip it over. A well made rug has a backing that's actually attached to the pile, not just printed on top of it, and the edges are bound or serged tight, not glued with something that'll crack and peel after a few vacuum passes. Wool or a good wool blend will hold its shape and spring back under furniture legs, where synthetic pile often flattens and stays flat, looking worn out before it's earned the right. Cheap ones also tend to bleed dye the first time something wet touches them, which I learned the hard way with a glass of sweet tea and a rug that was supposed to be "colorfast."
Before you order anything, measure the actual footprint you need, front legs of the sofa and chairs included, not just the open floor between them.