The Ascendant is a powerful close up fighter who can fly away from deadly foes. He is partially good for sieging bases with his ultimate and Terra Smash. He is a great hero killer with his Ravenous Dive which deals alot of damage and uses the target as a shield, only if you have more strength than the enemy hero. It can also be used to drop heroes where they cannot escape from and then they are free to get killed by spells and ranged attacks. He can improve units size, damage, health and abilities with his Abberation which also can heal the targeted unit and can be casted multiple times on a single unit, the Abberated unit can be kept alive longer and deal more damage by getting STR and INT items. Stone Gaze isn't that useful.
The two main abilities that i would suggest you should spend skill points into are Ravenous Dive and Terra Smash which are his main offense, if you want an ultimate that would deal more damage get into DIVE and Hell Fury and get an Orb of Skill or Talisman of the Sun (Artifact).
He can synergize with Emberwraith using Terra Smash to slow and Pyroclasm with the Emberwraith makes a good unit killer and they both can hurt buildings. Also with Corona and Hells Fury which can rip up bases.
A secondary combo would be with the Defiler and his ultimate that reduces the strength of STR heroes and then a Ravenous Dive to finish them off, the Defiler has damage over time spells which can also make quick work of heroes if repeatedly cast upon a hero.
Abberation is absolutely imba when cast on Lost Souls (instead of, say, an Abominations). The resulting unit has thousands of life, high armor, ranged attack (albeit with very slow attack speed), and most importantly, maintains it's ability to polymorph enemy units. Abberation skill is currently flawed, as computer controlled units under it's affect will not use the special abilities granted by this skill. Abberation works on Sorrow Liege's Royal Guard summons. Very useful, Royal Guards can redirect damage from nearby heroes to themselves, so a Royal Guard with several thousand life that can be fully healed with one cast of Abberation is very nice. Also, if I'm not mistaken, Royal Guards under human player control can be instructed to use the various bonus spells granted by Abberation.