The Spell Could be Considered Balanced
TL;DR: Not having concentration and the effects of "blocks line of sight" are what bother me.
To start, let's look at some comparable spells.
- Fog Cloud, which if cast as a third level spell obscures the friendlies in the area and requires concentration. Because of the third dimension, 60ft radius does give it amazing surface area by comparison. If your spell is 6ft tall (cover most character height), that still gives you a wall 200ft long, which is roughly a 32ft radius ring. So roughly half the dimensions if we're using a two dimensional map.
- It matches the area of Wall of Fire from a purely mathematical standpoint (60x20) which is a 4th level spell but also has the damage behind it, and requires concentration but has the one-way effect.
Now the illusion spells.
Level 2 we have Phantasmal Force (PHB264) which affects one target, limits to a ten foot cube but gives you the base effect you desire. It requires Concentration.
Level 3 Major Image which gives you a 20ft cube of "visual phenomenon" for up to 10 minutes but requires concentration.
Level 4 we have Hallucinatory Terrain which gives you a 150ft cube of look/smell/sound like a terrain of your choice for a day, but has a 10min casting time.
Notably the "field" type illusion spells above break when interacted with and affect allies.
- Invisibility does a lot of what you want but only affects two creatures if cast at level 3 and breaks on the first attack. One hour but needs concentration.
- Great Invisibility is level 4, requires concentration, only affects one friendly for up to a minute and doesn't break on action. Note: With the invisibility spells, it has the benefit of moving with the target(s), but does not inherently let people see obfuscated allies.
The main factor that puts me in favor of the spell being balanced is if the breakage of LOS is just about the disadvantage on attack rolls and not actual total cover. Invisibility rules still allow spell effects to target a space they can see which if they target the (flat) screen feels like it amounts to disadvantage to opponents if they have to make a spell attack roll but doesn't actually change anything if they're within an AOE.