Against the long list of games that have quite bad invisibility, in the shorter list of games that have gotten invisibility right though, TF2 stands out quite well in my opinion.
Summary inbound, if you’re familiar with TF2 just skip (or feel free to proof-check!)
[spoiler]When activating the cloak, Spy is completely invisible but unable to use guns or melee. This is till cloak runs out or when he himself decides to decloak, which takes about half a second and makes somewhat distinct sound, and then he can use whatever weapon he had on. Cloak would flicker when Spy bumped into enemies, so he can’t slip right next to any actually aware player without getting spotted and destroyded. He can use disguising to catch up his prey between decloaking in peace and approaching target. Spy is rather strong character, for that he is able to backstab (instakill when hit from behind) enemies with his short-ranged melee. There is also direct counter for him: Pyro who is able to set enemies on fire, making cloaked and disguised Spies completely visible when in flames and being able to push them away with airblast ability.[/spoiler]
/summary over
Now to Phantom. As someone said here, no one likes getting assasinated. Where that comes from? There can be as many reasons as there are assasinated players, but I feel it mostly comes down to feeling powerless against out-of-blue kills which you felt like you, no matter what you would’ve done differently, could’ve prevented. Obviously if you dwelve deep enough, you find stuff like positioning, awareness etc. but everyone cannot do everything at once. That powerlessness is what I feel is one of the main reasons of him being the odd one both after using Phantom and playing with/against them.
His cloak as it is now, doesn’t feel like fitting into fast paced game. It punishes you for moving fast, but if utilized so that you are completely still, you can have almost unpreventable hop on your enemy and that’s where I think people have the feeling he is bs. Almost unpreventable since yes, there is humming sound, but there is usually so much spam and noise all around the game going that it’s tough to catch. Awareness awareness yeah, stuff shouldn’t be made easymode but neither put too much distinctiveness into one counter.
I think this was one of the reasons SD wanted to add shield to it, to make movement punishment feel less discouraging, as compensation and preventing stray explosives & bullet spam being so extremely dangerous, but it just doesn’t have right feel to it. With invisibility he should already have advantage of repositioning himself in a way not possible for any other merc, so he should be able to dodge or least anticipate where most of the projectiles are going to be flying around.
Some peeps in forums all over have already suggested this, but simply making Phantom to exit his cloak manually with some kind of a distinct voice cue before attacking / interacting with anything would be worth trying. How about making Phantom, while invisible, stay that way no matter the speed he was going on land, but flicker greatly maybe right next to an enemy and when walljumping? How about removing shield but make him not be detected by mines when invisible and have gain Guardian Angel perk temporarily while using cloak, so it’s all upto himself to dodge those strikes instead of trusting the shield? I wouldn’t mind some sort of a spotting / disabling ability either given that he’s recon, but that’s completely another debate.