Xerath is very oom but the rework allow him to snipe a lot of things including buffs with huge range in general.

In the ancient civilization of Shurima, the mage called Xerath practiced magic with undying passion. He believed that with enough magical power, he could gaze into the heart of Runeterra to know the secrets of history and the universe beyond. Such magic was beyond the limitations of a mortal body, but Xerath obsessively pursued a path to infinite power nonetheless. With every breakthrough he grew more and more powerful, yet not without consequence. Xerath's increasing arcane abilities wrought havoc on his physical form. Desperate, he undertook a dangerous ritual to transcend his dying body. The outcome would be immortality or self-destruction. Violent magic unleashed during the ritual caused devastation throughout Shurima, but when the dust settled, Xerath emerged as an ascended being of pure arcane energy.Free of flesh and bone, Xerath held nearly infinite power at his command. However, in the wake of his chaotic ritual, the mages of Shurima feared his careless disregard for life would bring ruin to the kingdom. After a terrible struggle they subdued Xerath, but they could not destroy his ascended form. Instead they trapped him within an enchanted sarcophagus and sealed him in an underground tomb. Eons passed, civilizations rose and fell, and Xerath's imprisonment was lost to memory. For centuries, Xerath's vast power tore away at the sarcophagus and weakened its spell. Finally, he willed forth a burst of magic that shattered his prison, but its core remained, containing Xerath and his power within its broken pieces. Seeking to rid himself of this burden, he was drawn to the magic of Valoran's nexuses and found he could absorb their power. Yet the nexuses had gatekeepers: petty mages known as summoners. Xerath knew his key to true freedom from his prison lay in gaining their trust, and he offered his power to the League of Legends.

“I have no need for vengeance. Time has brought ruin to the mages of Shurima and I alone remain.”
―Xerath, the Magus Ascendant

I max q for maximum damage even though he was reworked and w and e seem stronger his q is still strongest as it deals good damage,low CD, and okay mana cost when everything else either hits only 1 target including minions or has to hit in the middle for most damage.It became a charge skill(vi's q) which I don't like but oh well same range as the old q with w when fully charged.
I max w second since though it kinda sucks unless you hit in the middle,but it's by far better than e now that it can hit minions and the stun is rather unreliable.decent range and aoe.
E is rather straight forward it just sends a ball that stuns enemy in contact with decent range hit at max range for max stun and etc.
His new ultimate is rather beast now with a huge range and reveals target,the only bad thing is it cause u to stun yourself for damage,range,and vision totally worth it.
His passive is rather okay for mana sustain as he has decent as range.I honestly liked the older one where you could survive ad assassins burst and maybe even carries but he was mana hungry so that is something that it changes but only by a little.

Pros
Good range
Good damage
Built in mana sustain
2 decent cc
Cons
Mana hungry
Easy to burst
Relies on AOE

Try to last hit with aa to save mana since he runs out really fast.Try to use q to push lane if you have to back.Also use w and use the bonus damage from the center as minions don't really move as much as champions.