Sven was one of the strongest carries in the game for a long time. But the newest update 7.06 gave him, even more boost in power by buffing it. Let's look at why it is so powerful.
As you can see, his stats is very high in the start of the game. He has 660 hp and 5 armor which makes him easy to lane without dying much. His high attack dmg plus quelling blade and fast attacking animation makes last hitting very easy. When the team picks no support and 5 carries, you can usually go against many offlaners solo, but it depends on enemy offlaner.
Storm hammer is the strongest stun in the game in my opinion. It can stun multiple enemy heroes as it has 225 radius which is pretty big. It also deals lot of damage in the early game if you scale it up well. It can also avoid linken sphere if you stun creep, neutral near enemy hero which has linken, it stuns them anyways.
This skill basically replaces and improves upon battle fury . Battle fury gives 40% cleave damage and costs 4500 gold to build whereas great cleave gives 66% cleave damage if its maxed. It enables sven to farm at very fast speed and allows him to clear ancient/camp stacks early on with his ult and cleave.
This ability makes him even tanker as it provides 20 armor that lasts 8 seconds. Bonus movement speed and armor helps him to escape quickly too. 
This ability makes his damage output skyrocket. It used to give 250% -300% damage increase before but now in 7.06, it gives 160% plus extra 36 strength which makes him super tanky even without tank items and increases his damage significantly even better than before because damage multiplier multiplies your strength.
Item Build:
Early game- buy 2 slippers of agility, quelling blade, tango and upgrade it into poorman shield from side shop when you reach your lane.
Mid game- Power threads into Mask of madness or Echo sabre and then go either Sange and Yasha or Blink dagger or Black king bar first in any order necessary.
Late game-Daedalous/bloothorn, assault cuirass and moonshard eat if maxed.
Talent best picks:
At lvl 10 get 225 mana, so that you can use all your skills later without running out of mana
At lvl 15 get 8 all stats because 20 movement speed is unnecessary
At lvl 20 get 30 attack speed usually but if enemy has many carries that has not yet built monkey king bar, get 20% invasion
At lvl 25 get 65 damage because most fight wont last that long to enable you to use 5 sec stun anyways
Synergising heroes:
Darkseer vacuum
Magnus empower and rp
Best versus:
Cleave is good against hitting multiple meepos and stun can interupt puff
Chaos kinght ultimate
Phantom lancer illusions
When laning, its very good against Weaver and good against basically all offlaners because of his stun and tankiness.
Follow, upvote me if you enjoyed and check out my other contents if you wish to.