Poppy needs some love! (Please read summoners/Riot!)
As all old summoners know, poppy used to be pretty bad because of her base stats. Riot being awesome as they are redid her kit.
Some of the changes are great, but others are just lacking, or not at all very helpful in team play. specifically her ultimate.
(R) Poppy ultimate has a giant windup that makes it widely visible she's trying to push someone back. There are a few flaws with this skill that I would like to list. Firstly as a tank/brawler is to absorb damage, and dish it out in front of her team. Having said that her ultimate moves enemy's, and potential kills AWAY from her team! Which you could say is helpful to make the team fight a 4v5. But that's not what anyone wants. We want all five kills for a penta/wipe! Which poppy ult denies you.
The second issue with it is it ONLY push's enemy's TOO their base! This not only ruins the potential gank utility of the skill, but also forces poppy or her team to position themselves according to her ult, which just isn't going to happen most of the time.
You also are FORCED to get used to holding R for a prolonged period instead of just tapping it which leads to many accidental ult fails. It should be set so when you HIT R that the skill starts to wind then you tap R again to use it!
Now that we have mentioned the weak points of her ultimate let's get down to her slam, this skill is amazing! You can push enemy's off your team, or into a wall for your allies to catch up! But it alas ALSO has an issue. The range is too short! Even with a ton of speed on poppy, and her W, you just simply cannot position her for a proper hit without a flash.
In my opinion the easiest way to fix her, is to simply dump her new ult (Which yes I know you worked hard on I am sorry!), and replace it with a taunt. By taunting enemy's to her she can not only defend her team, but also land her stuns better, and utilize her kit! This also would let her team do some serious damage before the action begins. I know most of the time these get blown off, but I hope my love of poppy,and her cute mug will inspire someone to leap to action! Defend poppy's honor! 
knock up except you should be able to choose the direction you want it to fling them (keeping the spirit of her HAMMMER!; not a charm, sorry). Her knock back is fine the way it is, it provides a bit of difficulty except that it is point and click. You should be able to dash through walls with her E (similar to Vi's Q), unfortunately we'll likely never see that kind of thing. Main Poppy, mastery 7, love her for life.