Consider this: The Wizard gets access to probably the most powerful spell list in DDO. A Wizard's spells can include:
-Some amounts of healing, including self-healing (via Repair for Warforged and Negative Energy for Undead forms)
-Summoning (sometimes useful for soloing or on lower difficulties - it's a distraction at least)
-Direct damage of every damage type, without needing to specialize in a type (fire, electricity, etc.) for maximum effectiveness like a Sorcerer
-Damage over time (Wall of Fire)
-Crowd control (charms, Web, and Hold are the biggest ones)
-Debuffs (Enervation, Energy Drain, Hypnotism, Cloudkill)
-Buffs for himself and his party/minions (Feather Fall, Haste, Resist Energy, Rage, Blur, Displacement, Protection from Energy...)
-The convenience of Dimension Door and two flavor of Teleport
-Utility spells (Knock, Jump)
-Save or die spells (Finger of Death, Wail of the Banshee)
-Access to most spell levels 1 character level sooner than a Sorcerer
-The ability to swap out his spells at every rest
-While not technically spells, a Wizard can get spell-like abilities of every school except Divination via Archmage and Pale Master (and the Wizard Past Life feat that requires a feat slot)
Also, there are other benefits to being a Wizard.
-A Wizard's primary stat is INT. This means a Wizard is likely to have (via tomes, race, and levels) one of the highest pools of skill points available by max level. With the feat Insightful Reflexes, a Wizard can have a kickin' high Reflex save.
-Not every Wizard spell requires the enemy to fail its save for the spell to be effective. Sometimes, blasting just works (even if other classes can DPS better)
-5 bonus feats - at Wizard levels 1, 5, 10, 15, and 20. This is tremendous compared to the Sorcerer's 0.
-There are two races (Drow and Sun Elf) which start with +2 INT. Both these races can get +2 more INT via enhancements, and are pretty spiffy for a Wizard. Both these races are not initially available, however.
-Humans (initially available to everyone) can get +INT (or +any stat), but to a lesser degree than the INT Elves. Also, humans get +1 feat at level 1.
-Warforged can make spiffy Wizards due to no INT penalty (though no INT bonus), but a higher CON (meaning more HP!), self-healing via Repair spells, and a host of immunities just by being Warforged. Some spiffiness goes away in Undead form, and Warforged require 1 AP to remove their racial arcane spell failure. High-end Wizard docents may be more difficult to find than high-end Wizard robes/body slot items.
-The Wizard class is free to all players.}
Downsides to being a Wizard include:
-You're probably squishy. Bluffs like Stoneskin, Blur, and DISPLACEMENT keep you alive. In this way, you're also somewhat buff dependent (or dependent on just being out of harm's way) to ensure your survival.
-Slightly longer spell cooldowns than a Sorcerer.
-Fewer spell points than a Sorcerer of equal level, ability scores, and gear. However, with the right setup, this drawback can be worked around.
-If you're in melee, it's probably because you're against a barrel.
-Very magic-dependent. Antimagic can quickly ruin your moment.
-Adding spells to your repertoire can get expensive. Can be worked around by proper planning and patience so you only get the spells you need and plan to use.
-Knowing what spells are optimal to pick at level up requires foreknowledge, and learning rare spells at level time may be at odds with spells you plan to use.