How is Tahm right now

Tahm, in my opinion, requires skill to play him properly; in the hands of a skilled user, he is extremely powerful and versatile. First off is your passive. You can get max stacks on your passive by literally hitting the same person three times in a row with your tongue lash. Your tongue lash deals a huge amount of damage, and is quite spammable. A flash-tongue lash combo can help your team catch up to enemies. Not to mention that if the botlane decides to engage on you, you can actually stun their adc. Devour is an extremely situational spell, but can save your adc from anything; and I mean, anything. Jinx rocket coming? Devour. Leona ult? Devour. Vi ult? Devour. In addition, during team fights you can literally remove a person from the fight for 3 seconds, or save your carry if they are being dived upon. Thick Skin, is for more survivability and substain. Tahm's ult makes his basic attacks deal insane magic damage when building full tank; if you build a Wit's End at the end of your full tank build, you can one versus one anyone in the game; ocassionaly, I'm also able to three shot the carry. The active portion is also strong, allowing your jungler a free trip for a gank or to secure objectives. So, I really recommend playing Tahm.

Annoying and hardish to kill... sounds like he is doing his job!

I love playing him, but I'd say his power level is a bit weak, especially outside of premade teams where no one uses his ult.