Devourers Intiation allows him to bring the enemies to him, for his team to destroy, instantly making it a 4 vs 5. That is far better than throwing yourself into 5 enemies. Don't get me wrong, it will be hard to farm, but you don't need to farm to use your abillities, You Rot, Hook, Ult. One enemy down (assuming team is there too).
Pharaoh - You go to your enemy stunning everyonein a smallish radius (300 or so i think) you have hell fire, good for ganking, puts you in the middle of a team fight.
Behemoth - best initiator there is.
Magmus - can intiatie with ult but then he is in the middle of 5 heroes (assuming no deaths)
Valk - Good stun, but it's a single target stun, and not the best for intiating, as you still have 4 other people to deal with.
Pebbles - Good stun, and chuck does alot of damage. No complaints
I said devourer was a good initiator, Most heroes can be agood ganker. Only Pudge and Andro can bring the enmy to them, and then disable them, however even andro has to place herself in the firing line.
i'm not saying he's the best hero ever, you are right about his lane presence being weak, the fact he can be harassed to great lengths. I am simply stating that he is not as useless as you seem to be making him out to be. Rampage for the worst hero
Rampage and NH are not useless. Good NH's are scary. Rampage can nearly stunlock someone with very few items (and kill them in the process). There's also 0 chance escaping a well built rampage without escape mechanisms or help.
Devourer is not useless. He's just ludicrously easy to feed and fail with. His hook is hard to land and noobs fail it pretty much all the time. Good devourers, like good NH's, are scary.
Why? You take 75dps from decay after basic magic armour. This is at about 20-25 minutes ingame. In a normal and even game, no carries have any big items yet (they should be very close to finishing one). 75 + 100 from devour for 3 seconds is 525 magic damage. That's as much as pyros' ult at level 2 or 3. It's also a 3 second disable. If you're hitting more then one person it starts stacking too.
If you give devourer mid, he's a beast, not because he can farm well (he can't >.>), but because he gains levels quicker then in a double lane. This lets him gank faster. A level 7 devour coming up behind you when you're level 5 is not fun, since you have 2 choices. One, run at devourer and die. Two, run at the 2 people you're laning against (and who are now charging at you) and die. Not fun.
And his ability, as others have mentioned, to turn teamfights into a 5v4 is not to be underestimated. If his team is right near, anyone he hooks will explode, instantly, with no hope of survival. Only 2 other heroes in the game can do this, and one is probably going to die in the process.
Anyone that says Slither / Torturer / Ophelia is bad is in fact...bad.
Slither scales terribly, he is very effective early and is a great ganker, however mid/late game he becomes more support oriented where the more "useful" heroes come into play.
Also, his DoTs make it very easy for him to have his kill denied and are all removable with defusal.
With that being said, Slither shouldn't be getting kills in the first place, he should be setting them up for heroes that can actually benefit from them.(any decent carry)
Similar to the way Int heroes should be setting kills for your carry heroes, rather than using your nuke to get a kill in a gank the enemy has NO way of getting away from.(Think Pyro/Lion/TB here)
Lol at all the dev's bashers. In the right hand, dev is extremely powerful. Lets not talk about whether he can gank a lot of ppl early game or not, just the simple str bonus he receive from third skill is already make him decent. As long as a dev doesnt feed too much he gonna end up with tons of hp, high mdef and his ulti is a 3sec disable that goes through shrunken head. He is really decent even at end game as he can picking off ppl before team fight even begin (usually forcing enemies to jump in to save their friends and fight under disadvantages) and disable important targets (ulti got pretty low cd also help a lot).