4e is actually pretty easy to learn, despite my massive wall of text below. WotC may have pruned and streamlined things a bunch, but every character is built the same way, save different powers and such. Combat has a bit more "miniature orientented, but with PbP games, no need to buy that stuff.
Probably the *biggest* change from 3.5 to 4e is the introduction of turn, encounter, and daily powers.
At level 1, a character has 2 or 3 turn powers, 1 encounter power, and 1 daily power. Turn powers are things you can do every turn (a warrior can cleave or power attack), an encounter power is something that can be used once per encounter/fight/5minutes (warrior's viper strike, which does more damage to the target, and can prevent an enemy from moving around) and daily powers (can only be used once per day or extended rest). Dailies are the big signature moves, that *usually* grant some kind of effect even if you miss your attack. Some grant 3W damage and are reliable (roll your weapon's damage die 3 times, you dont expend the power if you miss), some grant half damage, some make area effects, etc. And there are some dailies that are *really* powerful that are all or nothing affairs. As a wizard, you'd probably have 4 or 5 spells a day at level 1 in 3.5e. In 4e, your spells are the turn, encounter, and daily powers. Magic missile is a turn power and thus can be cast *all day long*. Flaming hands, *every five minutes*. Fireball? Acid Arrow? every day.
As you level up, you get access to new powers and add more to your pool of abilities and you can switch out powers from the list you have available to you. I'll admit you dont get mechanical deviation of such orders of magnitude as 3.5e, but there are builds and power choices available to each class. With things in the PHB1, You can make a wizard be a nuker or an AOE controller, fighters can Sword 'n Board or Two-hand it, warlocks can be made damage over time or debilitators, etc.
Another thing WotC did was split the classes into groups. Defenders, Leaders, Strikers, and Controllers. Defenders are your typical fighters, paladins, meat shields. Leaders are Clerics, Artificers, Warlords, peeps that heal. Strikers are your Rogues, Rangers, Warlocks, damage dealers. Controllers are your Wizards, Invokers, Druids (now?), area of effect peeps. Each class has a different power source (martial, arcane, divine, primal) that gives the overall flavor and fluff of how you do a particular job. Looking at leaders, Clerics are your divine healers and zombie smashers, Artificers attack from a distance and give buffs and arcane healing with magic devices, Warlords are like sergeants that allow for tactical advantage on the battlefield and inspire your team to push on and dig deeper than they thought they could (healing).
Plus, WotC has made a character generator program to help build characters in like.. 2minutes? *much* better than flipping through pages, I asure you.
All that said, Im thinking of an artificer. I'll get him posted later today.