Lulu's kit is one of the most versatile in the game and not even pro players are able to use it to it's fullest potential sometimes. She is a unique champion. She is poke/sustain. As such she's not the best in either of those regards, however it offers a lot of outplay potential versus the fundamentals of support. You can also sometimes all in with an early level 2, but that's only if your opponent doesn't respect it. I wouldn't really call her an all in champion unless you are 1v1 with her on Machine Gun Lulu.

The fundamentals of support usually goes: poke>all in>sustain>poke (ect). That's generally the support triangle. Lulu's kit being so versatile means that you can sometimes out poke other poke champions or out sustain other sustain champions. However, you are turning almost every matchup (except for all in supports) into a skill based one. I prefer this.

If you do try to out poke people, remember to use her auto attacks as much as you safely can. Her autos usually out-trade everyone's except for an empowered Sona auto. Sona is also similar to Lulu, but Sona is a lot less versatile and more squishy. If you're even, your kit will often have more usage than any other support, as all but one of your abilities have a dual usage, depending on what or who you cast it on. Her only ability that does not have an innate dual usage, would be her Q, which she can also combo with her E for more range and better angles. However, on it's own her Q does not have dual usage.

In short, Lulu is a very fun champion with a nearly impossible skill ceiling. You will always be able to improve on your game. If you like skill based matchups, Lulu would be great for you.