Poppy is a very versatile and overall strong champion. She can be played AP, AD, and I've even seen her played as a tank effectively. She, next to Shaco, is in the top bracket for needing a re-work to even out her play style now that we have Dominion. The biggest problem I find is that she can be built into a burst champion who can not be burst themselves. Now I know that your team should CC her so that you can whittle her down but she has two skills that make this difficult, a defensive movement skill and her ultimate. Without many true damage champions or items out their to counter her I just feel that she needs some kind of rework with her passive or ultimate to even out the new game play that we undergo playing Dominion.

With Poppy's Ultimate lasting 6/7/8 seconds Riot needs to do something to fix this as it is just to long for Dominion game time seconds. Making a new Dominion item similar to the quick silver sash may be an option so as not to mess with Summoners Rift game play while trying to fix the problem.

I honestly think that Poppy is completely fine unchanged. Like any other champion on any map, she can either be extremely powerful, or fairly bad depending on who plays her, who her team consists of, and who the other team consists of.

I have played against Poppy's who do extremely well on Dominion, but I still have been able to kill her by myself by using the right tactics.

In general, the object of Dominion is to use team work to keep 3 bases or more, and to defeat the other team. If Poppy is somehow OP on the map, she herself cannot counter a full team to win on that map.

I suppose what I am trying to say is that although she can be powerful on this map, so can many other champions and I believe she is fine the way she is.

how about a nullfire blade? active removes debuff from allies and bufffs from enemies. 60s CD ???

with a team, no
without, yes

The vast majority of Poppy's damage comes from her charge/%dmg attack. Build some HP and MR, and always make sure you have some CC near you.

if i ever see poppy picked i always know how to counter her, its called olaf insane amounts of lifesteal means he beats anyone 1v1, and when she gets low and her passive starts to kick in i use my e to deal 350 true damage and just kill her.

poppy is not problematic you just need to counterpick her

Poppy is pretty easily countered with MR. She still bursts hard, but she's manageable.

Avoid getting walled and avoid using big bursty nukes on her. Pretty simple stuff. Crowd controls also neuter her ultimate quite a bit; this is generally true of characters with ults like Poppy such as Tryndamere, etc.

EDIT:

Also, because you mentioned Shaco as a problem; play him. I'm serious. He's really not a problem. He's really a kitten and not very dangerous most of the time. The boxes are silly, but that's all they are. He's a gimmick more than a real serious problem pick.

poppy has a problem which will help you counter it

in a nutshell
AP poppy = Magic resist
AD Poppy = Armor

In a bigger nutshell
AP Poppy that cant one shot you = useless
AD Poppy on the other hand will have much lower damaged Q and E, giving you more time to beat her up

And one big tip to fight poppy? QSS / Cleanse
Wall slam > Stun > Remove Stun > Run away > Poppy Ult down > Beat her up
Works 99% of the time

And last thing, do not stand too close to wall when she is coming...

And I have my own counter for Shaco too, but he is stronger then Poppy, I must say