Okay, let's just pause for a moment before I dig into the nitty gritty. I like Symmetra - I really do, and I'm a little hesitant to create this breakdown because I have a feeling I'm going to upset some Symmetra mains out there. I think she's quite viable in certain situations, and she's a ton of fun to play. At lower tiers of play she's can be a serious force to be reckoned with. If you truly want to play effectively as Symmetra, you need to keep the following in mind.
Symmetra (right now) is not really viable when playing with an attacking team, with the exception of Control maps (Nepal, Oasis, Lijiang Tower and Illios), provided she is not up against multiple heroes that effectively counter her. Effective counters to Symmetra include Winston, Roadhog, Pharah and Junkrat, and anyone who has good aim at range (Widowmaker, Hanzo, McCree, Bastion, Ana and Soldier 76). A good Tracer can typically defeat Symmetra one on one, as can a good Brigitte.
Can Symmetra be played on attack? Certainly, but there are other heroes who would be so much more useful, and if the defending team has more than one hero that counters Symmetra, it would probably be a good idea to switch, especially if you keep finding yourself in the spawn room over and over again.
Don't get me wrong. Symmetra can be awesome when used correctly, but what many players find as they start to run into other players who have more experience dealing with Symmetra is that there are a lot of ways to counter her that she cannot deal with easily. In theory, you could "main" Symmetra by spending the majority of your time playing as this hero, but you should also be playing other heroes in situations where Symmetra is struggling. Unfortunately, those situations are quite common, especially against experienced players.
Let's start with the basic weaknesses of this hero. Symmetra is not very mobile because she moves about as slowly as a tank, and does not have any abilities that allow her to easily evade incoming attacks. The only thing she has to save her is a shield projection that travels forward in a straight line until it comes into contact with a physical object in the map terrain, upon which point it disintegrates. Use of this ability comes with a 10 second cooldown, which means if Symmetra is dealing with enemies attacking from multiple directions she can only use the shield projection to defend herself from one of them, and only temporarily at that.
Symmetra's primary attack (photon beam), while deadly once it has been charged up, has a very limited range to establish a connection to a target. Her target must be at least seven meters away before a connection is established, and if her target is more than ten meters away or breaks line of sight for longer than a second, that connection breaks. Taking into consideration Symmetra's mobility, this only gives her the opportunity to do massive damage brawling while her team is battling it out at close range with the enemy. When she's on her own, unless the enemy team doesn't see her coming, it is not very effective.
Energy ball, her secondary fire, creates a slow moving projectile that can pass through heroes as it damages them. She can charge it up to create larger, more damaging projectiles to do up to 125 damage per hit. At higher levels of play, these projectiles are easily avoided, and when facing off against a D.Va deploying Shield Matrix, they are completely useless.
At higher tiers of play, Symmetra's sentries are only useful for a limited time, because once the element of surprise has worn off they are usually quickly destroyed. There is also a cooldown timer once the first six have been deployed, so a rapid destruction of her sentries reduces her effectiveness as a damaging team member.
Finally her two ultimates are the only ultimates in the game that can potentially last for an entire match, or be shut down immediately. The biggest weakness of teleporter or shield generator is that they are stationary and can be destroyed relatively easily once they have been found. Teleporter is usually of no use in the later part of a match due to spawn advantage for the defending team. Shield generator only offers an extra 75 health in the form of shielding to your teammates, and only regenerates that shield buff after they stop taking damage. Lastly, should you decide to switch to another hero, your shield generator or teleporter will vanish immediately.
So how do you play around these weaknesses? Let's start with the sentries.
You should only cluster more than three sentries together when you are absolutely certain enemy team members will need to pass close enough to them for a lock-on. Avoid clustering them together in a straight line (it's easier for the enemy to shoot them down if they are in a row).
When playing with the Defense team, I will take Symmetra all the way to the enemy's spawn room and quickly set up three sentries at two of the doorways, or three on either side of the main doorway. I will then head back toward my team a certain distance - just enough to still be able to see that main doorway but also make it back to my team before the enemy dives on me with their agile heroes. I will lob a few fully charged energy ball orbs straight at the doorway as the timer counts down from five seconds to start the match. The combined damage from the sentries and orbs is usually enough to bring my ult charge over 40% within those first few seconds of the map. I have played matches where I unlocked my ultimate with the first 10 seconds of play.Watch Symmetra - How to Build Ult Fast on Hollywood Defense from Wyrdsmyth on www.twitch.tv
The downside to this tactic is the sentries are usually quickly destroyed, and at most I will be able to place three more before the attacking team runs into our defense. Then I'm at the mercy of sentry cooldowns, but if I keep my head and stay away from the attackers, use cover and quickly place sentries in smart locations, I can switch from building to directly assisting my team. Even if I'm killed by the attacking team, usually by this point I will have unlocked Symmetra's ultimate and can either set up a teleporter or shield generator on my way back from spawn, depending on what seems most useful.
At this stage, when placing sentries you should try to keep track of where they were last placed, and avoid placing them back in the same locations. The enemy will expect them there and quickly destroy them again. It's better to find new placements to reintroduce that element of surprise. One exception to this rule, however, is the ceiling of the capture point in Ilios, on the Lighthouse map. It's very hard to clear the sentries from that ceiling if they are scattered all around, and it is extremely difficult to survive if you enter that capture point while there are so many sentries present.Watch Symmetra - Sentry Play of the Game on Illios from Wyrdsmyth on www.twitch.tv
Also, take advantage of objects in the environment. Several maps have plants that can make it harder for the sentries to be seen. A few also have crates (Temple of Anubis) where a sentry can be completely hidden but still be effective.
Energy ball, even though it is slow moving, is still potentially devastating when used correctly. Symmetra can take advantage of walls, the payload or other cover to charge up an energy ball to full strength, and then release it at point blank range into a nearby enemy. This is particularly devastating for tanks because it passes through shields and ignores armor. It also passes through multiple enemies, so potentially it can damage multiple enemies in a single shot. Three shots followed up with Photon Beam is usually enough to take down most tanks, provided they are not focusing Symmetra.Watch Symmetra - Anubis Play of the Game - Earthshatter Shutdown from Wyrdsmyth on www.twitch.tv
Teleporter can be used to great effect when an attacking team is trying to quickly rush to the objective, and in a two capture-point map can offset the spawn-advantage of the defending team at the second point. Shield generator can often times be just enough advantage for your teammates when they were previously getting wiped out too easily by the enemy team - just enough to rally and overcome that adversity when they were previously struggling.
Photon beam is potentially the most deadly attack in the game due to the increasing amount of damage it delivers the longer it maintains a connection. Even though it does not pass through shields, it can still be charged up against a shield (or a Mei ice wall), and will quickly eliminate squishies once fully charged. If you are playing with the team and focusing enemies, they will fall almost instantly. If you are flanking from the side or behind and remain unseen, you can easily take out multiple heroes before you are stopped, if you are stopped at all. Also, if you stop taking damage, your shield will slowly regenerate. It's not quite as good as Mercy's self healing but it can definitely help keep Symmetra alive longer than people might expect.Watch Symmetra - Dorado Defense Play of the Game from Wyrdsmyth on www.twitch.tv
Shield projector should be held in reserve, and not thrown willy nilly around the map. A smart Symmetra can save her team from a D.Va, Pharah or McCree ultimate by flinging the shield at them before they open fire (or the meka detonates). It can also be the extra level of protection she needs to survive just long enough when focusing an opponent in a one versus one situation.
Smart Symmetras stay alive and help their team mop up enemies. They play it safe, use cover, set up sentries in triangular patterns to make it harder for them to be shot down, and keep an eye on the match at all times. They build ultimate charge as quickly as possible to be as useful as possible to their team. They deploy their sheild projector at the best possible moment to maximize its usefulness.
Most of all, good Symmetras think.Watch Symmetra - Yet Another Anubis Defense Play of the Game from Wyrdsmyth on www.twitch.tv