I'm alive! :DMy opinions of specials that need buffs:
Revenant's Launcher: In theory, it's a potentially useful weapon for its ability to target specific spots, especially useful in Nightmare! for getting rid of that corpse in the middle of the room you would be otherwise unable to reach, but in practice, I find I never use it. As Evilpotatoe said, it takes too long to reload and I'd rather have a rocket launcher which I can mod.
Acid-Spitter: I think I'd like this weapon better if it didn't have to be completely full to fire and didn't discharge all of its ammo at once, like if it used one ammo at a time with smaller acid splashes. That would make it more versatile. As it is, situations where its useful are too rare for it to be worth the inventory slot.
Medical Powerarmor: I've said it before, but I'll say it again: If my health is below 25% and I have no other way to heal, I'm probably about to die anyway. Also, if you've taken enough of a beating to be that low on health, it's unlikely that your armour will be in good enough shape to use its durability to heal you and the only way around that would be to switch to this armour only when you're low on health, but who's going to switch in the middle of a fire fight? There's just no situation where this armour is useful, in my opinion. I think it should, at the very least, heal you up to 50%. (All of this applies to the regular medical armour too)
Megabuster: As it is, there's too much randomness to make this a reliable weapon. I like Evilpotatoe's idea of making firing mode manually changeable. (It fits better with the theme of Megaman's gun too) Another possible idea for your consideration: What if you could switch ammo types that it uses too? A weapon that could fire all four ammo types could be very interesting, though it would probably be overpowered unless it has reduced efficiency or something. Maybe you could make it a kind of "Jack of all trades, master of none" kind of weapon, a good back-up to have in case you run out of your preferred ammo type. (Side note: I don't particularly mind the Megabuster being overpowered, since Megaman is basically one of my all time favourite games ever) :D
Charch's Null Pointer: What does this weapon even do?!? :| I've read the description on the Wiki and it sounds like it's supposed to slow enemies down for one second? (Someone please correct me if I'm misunderstanding this) But in practice, even with sustained fire at a single enemy, they keep coming at me, seemingly at the same speed. (From the description on the Wiki, I would've thought that sustained fire would completely stop them from moving) I get that this weapon was thrown in as a programming joke, ("The Demon crashes" is a funny line) :) but it would be nice if it had some usefulness too like maybe it could permanently reduce an enemy's speed, or at least use less ammo? (p.s. who is Charch, anyway?)
Mjollnir: I like the idea of a melee weapon that you have unlimited ability to throw, (one of my favourite weapons to use in Nethack) :) but this one definitely needs a buff. As it is, it does less damage than a bulk-modded combat knife, so I'd like the damage increased. (with maybe a message like "Lightning strikes the Demon!") :D The current throwing range could be increased too; as it is, generally speaking, if you're using a melee build, and your target is 5 tiles away, you might as well just run over there and for any other build, you'd be better off just shooting them with a regular weapon.
Frag Shotgun: Please reduce the firing time. This could be a useful weapon if it didn't fire so slowly. As it is, I'd much rather use a chaingun for my bullets, so the only situation I would use this weapon is if I was playing Angel of Shotgunnery, and even then, only if I was truly desperate and somehow completely ran out of shells, because having a weapon that fires so slowly is very dangerous. The slow firing time completely kills any usefulness of this weapon.
Plasma Shotgun: Just a reminder that you probably want to fix the full reload bug. (As much fun as it is to exploit) :D
Combat Translocator: Only mentioning this one because Evilpotatoe brought it up. There have been a couple of occasions that I've put it to use, like sending away a Cyberdemon I didn't want to deal with yet in Angel of 100, but it's true that it's very situational and in most cases, I'd rather use that inventory slot for something else. I like the idea of a weapon that isn't "actually a weapon," (probably could do with some more, actually) but I'm not sure how this could be altered to make it fit in better. (Come to think of it, it would be really nice to find this in an Angel of Humanity game to help me isolate troublesome enemies) :) I'd be tempted to just leave this weapon as it is.
As for new unique/exotic suggestions... I've had the idea rattling around in my brain for a while of having "Boots of Butt-kicking." (Doesn't actually have to be called that) :P Boots that double your melee damage for fists only and no other melee weapons. (Doesn't have to be doubled; maybe just increased a little) It makes sense to me that if Doomguy has some hardy boots on, he would probably be kicking his enemies rather than punching them. (this doesn't mean I'm suggesting dialogue changes; "you hit the demon" still works fine and it would probably be too much trouble to change it to "you kick the demon") I imagine this could work well as an exotic item to complement your arsenal, or as a unique, in which case it could possibly have a small speed boost too? (10%?) And when you pick them up, it could say something like, "You feel like kicking ass," or "It's time to kick ass!" :) (And if you want to call them the "Tormuse boots," I have no objection) :D