I'd say Yone has perhaps the best engage/disengage ability in the game. As long as you don't die and time it right, your E can be a free engage that could let you make a stupid play but not get killed for it. You E under your tower, Q dash at the enemy, chase them down and never hit them once, even following them under their tower, you then return to your body and recall. That was in no way a good play, and you didn't get anything out of it, but if you were any other champ and not in your spirit form, you easily could have and should have died doing that. While in Spirit form, if you press E to return at any point you're getting CC'd, it will most likely be cancelled (with some exceptions like Veigar E). If Zoe hits you with her sleep bubble, when you press E to return to your body, if you would have gone from drowsy to asleep at any point before reaching your body, you will be unaffected by her CC. It can be hard for some abilities, Ahri's Charm for example, you have to hit E essentially just before the ability hits you, otherwise your spirit form will be charmed.
Yone scales exceptionally well. You could have been hard stomped in lane, but if you and your team stall the game out so you can catch up and get some items, you'd think you were the one stomping the whole game. It's something he has in common with his brother, the joke "when Yasuo hits his 1/10 power spike" applies to Yone as well.

While Yone is still considered very broken, he does have some major weaknesses. For one, his early game is fairly weak. While buying a 1100 pair of boots (Berserker's) makes quite a difference for Yone, the attack speed is purely allowing him use his Q and W slightly faster. He doesn't have any threatening damage until you buy Zeal, and that's if you're even or ahead of your opponent. If you're far enough behind, you tend to not feel like much of a champ until you build Infinity Edge. If your opponent can and knows how to abuse your weak early game, you might have to wait and hope you and your team will be able to stall out for you to scale back up.
Yone isn't particularly mobile, yes he has a dash, but it doesn't cover much distance and you need to land 2 other Qs to get it ready so it's not reliable as a disengage tool. This makes you pretty susceptible to ganks, and pushing the wave up and being extended in lane to CS is dangerous if you don't know where the enemy jungler is. Early on, if you see the enemy jungler is about to come in and gank you from your ward, to get your dash ready, you have to Q something (likely an enemy minion) wait at least 2 seconds, Q another one, wait another 2 seconds, and now you can dash. You're waiting at least 4 seconds to get your dash ready, at which point the enemy jungler is likely on you already, most likely in those first 2 seconds, or your enemy mid CC'd you, making it even easier for you to die in this gank. Best case scenario, you'll probably burn flash to escape if your jungler wasn't there and ready to counter gank. You could be using your E to extend with the lane pushed up, but if you're in a poke match up where you need your E to engage, you are instead using it to collect however many minions within the 5 seconds it's active, then you'll have to wait for it's 22-16 second cool down.
You are also quite susceptible to CC. This might sound odd since your E allows you to pretty much negate any and all CC. While you do have the ability to minimize CC effectiveness, if your real body is hit by CC, or you don't recast your E to escape it in time, you are just free for the enemy team to attack and you're a bit more of a squishy champ, so that second or two of CC can be enough to kill you.
Your Ult can easily put you in a position you don't want to be in, which is typically why I'll only use it when I'm in my spirit form. If you're not in spirit form, if you were to try and ult the entire enemy team, if you miss, they all flash, use some kind of dash, or possibly just walk out of your ult, or you even only get 1 or 2 of them, you are now in the middle of the entire enemy team with no way out. Even if you did catch them all, if your team wasn't ready to wipe them out right then and there, chances are they'll just turn, use their CC on you, just kill you in an instant. In your spirit form, you can ult them, whether you hit or miss them, you can recast E back to safety.

Also, a tip for newer Yone players, you will likely want to use your E as some kind of dash or disengage, as in you'll be going in and fighting someone then want to disengage with your E's first cast, purely like an involuntary reaction. It's a habit you will want to break ASAP. There are ways to make your E send your real body over a wall to safety, so aside from that and maybe other specific situations, it is generally just used for engaging.

A very basic "Quick Burst Combo" is Auto Attack>Q>W then you back off. You should be doing these three attacks within a second, so you're dealing a good amount of damage quickly and the shield you get from W should eat most of the damage your opponent deals while attempting to trade back.

The most basic combo is going into your E and using your Q dash. Q>Q>E>Q-Dash>W. The first two Qs could be on the minions, likely will be, at least early in the game. If you are doing this combo solely on an enemy champion, you should definitely be landing auto attacks against them between your Qs. Landing that Q dash in your E will immediately apply the effects of your E, which is to repeat an amount of damage you deal while in spirit form when you return to your body. Using your W lets you trade more since you'll have a shield, plus you're easily applying more damage to be repeated. It's easy to over extend yourself and enter turret range because this is also a pretty obvious combo, which is also why using W can be helpful. If you aren't over extended, the shield can help you continue trading and hopefully get another Q in (during early game where your Q CD is 4 seconds) before returning to your body.

An extended trade combo is E>Q>W>Auto>Auto>Q>E. The difficult thing with this combo is since you're engaging with your E, either you'll be approaching your opponent in your spirit form and they won't just stand there to let you attack them so you might not have enough time to do the full combo, or your real body will be fairly far up in lane and you'll be susceptible if any other enemy shows up or your opponent is able to follow up on attacking your real body (Leblanc is fairly good at this). The one upside to the latter is that since you landed 2 Qs before recasting E, your dash should be ready once you return, meaning if an enemy is waiting at your body you can dash through them and escape, otherwise you could use that dash to chase your opponent some more if you believe you can finish them off.

Q>Q>E>Q-Dash>R>W similar to the first, basic combo, just with your ult added in. Your ult takes a moment before it's executed, so it's fairly easy to flash, dash, and for some champs even walk out of. Landing your Q-Dash to knock up your enemy means they can't do anything to get out of your ult's hit box. You can follow this up with your W as well. This is a generally safer All-In Combo, you use it when you're certain landing all of these and some auto attacks will finish your opponent, and since you're in your E, if you mess up you won't be in a place to get killed for it.

A more dangerous All-in combo actually starts with your ult, which is R>E>Q>W>Auto>Q>Auto>E>Q. This one is more difficult to pull off for a variety of reasons. For one, you are straight out engaging with your ult before using your E, so if you weren't cautious and waited until you knew the enemy jungler was in another lane, even if you hit your opponent with it you're very susceptible to a gank. Of course if you miss your ult, which could be easy since you're not knocking them up beforehand, you will put yourself in a bad position, and anyone with CC could just use it on you right there. Same goes for how your E is a part of this combo, if you were using this in lane, say when both minion waves are at about the middle, you are ulting to then Eing on the enemies side of the lane, meaning your real body will likely be left on that side too, again, making it very easy for the enemy jungler to come out and attack you. There is the fact that since you should have your dash ready once you return to your body, you should hopefully knock any enemies up to help you get away. Later on when you have enough attack speed to make your Q cool down really low, you could start this combo off with a dash in order to ensure you land your ult, then do the rest of the combo as normal.

You can also use Yone's abilities with flash, with some having more specific situations. Flashing to land Q and W are some simple ones that you could use whenever it's appropriate, such as if it leads to you engaging in a trade which you can kill your opponent. This is also useful for engaging in team fights, such as using E to enter spirit form, approach the team fight (ideally a few grouped up enemy champs), flash towards them and press R to get them all. One explicit combo for this is E>Flash>R>Q>W>Auto>Q>E. Something a lot of Yone's combos have in common is that you'll have your dash at the end of the combo, which gives you room to react to however the situation plays out. If when you perform this previously stated team fight engage combo, if you used this on 3 or 4 enemies and the last enemy champ was separated and took this opportunity to approach your real body, you have your dash ready to get away or attack them, starting this fight in your favor by interrupting them. Another possibility is that doing this combo and ulting the enemy team gave your teammates enough time to show up and further engage on them, so you can now dash back into the fight to keep helping.