I've been maining Rakan since he was released. He is unbelievably fun. If you are looking for anew support to play, he'll meet any expectations you have.

I've been criticized for two things about my choice of summoner spells:

No Flash

No Exhaust

I've tried using both spells.
Any time flash could have gotten me out of a situation, so would my W, my E, my R, or my Talisman of Ascension. All of them have shorter cooldowns, and also give other bonus affects to either help my team or me do more, be it speed to everyone, a charm, a knock-up or a shield, i just find flash useless in comparison.
It's similar with Exhaust. I have enough CC that it won't matter.

One concern people have is the lack of boots in this build. The movement speed is covered by Masteries as well as other items. In game you are often still faster than everyone else, and if not faster, then still more mobile.

With heals, CC, and being a tank, massive mobility, and having one of the best engages of any champion, Rakan is amazing at team fights. He can work with his team separately to stop enemies from getting away, saving teammates from dying or just giving vision. His teammates can also help him by being in range of his E, so that he can get out of a fight when running away.

Rakan and Xayah Work extremely well together (as intended). Rakan's E range is doubled with Xayah allowing him to be far more reckless and pull some pretty annoying things with baiting and escaping. When Xayah uses her W (Deadly Plumage) Rakan also gets the attacks speed/damage buff if he's nearby. The recall bonus is also great. Xayah and Rakan can recall together, leaving at the time the first one started the recall, leading for some pretty mean escapes assuming one is behind the other.

The last unique part is if Xayah and Rakan dance next to one another, they dance together, which looks very interesting if spammed by both people, or elegant if both players just let the dance happen.

The Pros are consisted of all the things above.

The only cons to playing Rakan are that most people don't seem to understand how he heals, and how his E works.
[*] After his Q hits A Champion, a Drake, Rift Herald, or Baron Nashor, he gets a ring around his feat. after a few seconds it will burst healing him and up to 1 allied champion if they are extremely close. If he comes in contact with an allied champion before then, it will burst early healing both of them. Make sure your ADC understands how this works.
[*] Other champions can save Rakan by simply being in range of his E. If it seems both players are going to die, and Rakan is a bit behind, the one who is ahead can slow down just for a second allowing Rakan to E to them, and then both players will likely live, instead of just 1.