That actually sounds amazing if you're playing with a close friend.
One of the fantastic designs of SS2 is that theres a lot of stuff you will NEVER get to use or access on your own. No matter what you pick, you miss out on something else. So presumably for multiplayer this means that every player gets to have their moment. Whether you beat down lots of hybrids and then it's, "Step aside, I got this one" as you blow them away with an EMP. Or hack a weapons cache otherwise inaccessible. Or Psi Pull that bag of potato chips...
Yup. Psi powers are interesting in that they unlock some entirely unique abilities like teleportation, telekinesis, invisibility etc - but also some abilities that are found elsewhere in the game (recharging items, replicating items, stasis) with an unusual twist (you never run short of energy if you have spare psi points; can replicate any ammo/hypo you want and not just the limited replicator menu; stasis without the inventory space needed for the weapon version).
Deck 4 has a bit of a hike in the difficulty curve - new tougher enemies and the hacks get harder. So my existing roles in my current co-op game have become harder to fulfill as I'm no longer capable of combat (and wasn't that hot to begin with as offensive psi attacks are weak) and it takes me ages to hack anything. But now I've unlocked tier 3 psi and can recharge my wingman's implants, power armour and laser pistols as needed, as well as duplicate extra armour piercing rounds which we're running short on. So that's offset my sudden drop in performance with my other abilities :D
(I'm still a pack-rat as well, pure-psis have a lot of spare inventory space to hold the extra gear)
In general, co-op can be a lot of fun with the right mindset. We have the music turned off to keep the atmosphere tense (the music is good, but not conducive to getting us suitably freaked out), we have Facetime on to act as our comms - and we aren't afraid to split up (which for a horror setting is indeed not at all smart, but when it goes wrong we get a nice little adrenaline buzz sprinting to reinforce the other, or frantically pulling up the map to find the nearest security reset before every hybrid on the level tries to get us).
Yeah now I'm excited and have to get my friends to play with me. =) I hope they made multiplayer in GOG much more stable as I recall trying it to constant disconnects back in the windows xp era.
We've just hit Deck 5 (having done Deck 4) and have had only one outright crash to desktop so far. It's also a good idea to save before level changes as it can occasionally fail to load for one player, requiring a disconnect and restart.
But it's much easier to use than it used to be. Fire up Hamachi and the game will connect to the allocated IP addresses first time. (Not entirely sure if Hamachi is even necessary from what I heard, but it's worked fine for us.)