3.5 really wasn't that different from 3.0. That's why they didn't do 4th ed right then. They didn't have THAT many changes to make..to justify a completely new edition I think. I haven't done much pre-3.0.. But I heard first ed and second ed were completely different games.. I'm actually getting really excited about 4th ed... HM.. I really need to go get the PHB and the DMG at least..
Well for starts, BAB per level is gone. Attacks are based off STR, INT, or DEX usually (Melee attacks STR, Magic Attacks INT, Ranged attacks DEX), so whatever your modifier is, thats your base attack bonus. Theres still skills and many of the feats are the same.
Secondly, every class has a set of "exploits" they get to use, these are At-Will powers (use per round as you see fit), Encounter Powers (once per fight), Daily Powers (once per "day", or until you take a full rest), and Utility Powers (usually triggered effects, often considered Interrupts). At first level you gain two at-wills (or 3 if youre a human), 1 encounter and 1 daily, and as you progress in levels you get more or can switch them out. A daily is basically your 2-hour. Does a large amount of damage but its use is limited to once per day. A save-your-ass move.
Third, you have Second Wind and the other things called Healing Surges. Every class gets these. Using your second wind uses one surge, and you can only use that once per encounter; but many classes have abilities that make you spend a surge to gain hitpoints back. Your number of surges is determined by your class and your Constitution Modifier.
New also are "Senses" which are "Passive Insight" and "Passive Perception", both of which, as a house rule, I dont use. What it does is it takes your Insight or Perception score and has you "take 10" on it, so its your score +10, usually somewhere around 16-19 on a 1st level character. It basically means your character is "always aware" of his surroundings, which I think blows ass. When you got a heroic tier trap (DC 15-20) and the bastard has a 19 passive perception, he automatically knows that the floor is trapped. Lame. It was made to make the game go quicker, so you dont have to needlessly search the room or call out that youre making a perception check; its automatically assumed you would. To hell with that. RP mofo.
Then you have the Dragonborn, Tiefling, and Eladrin races. You might remember Tiefling and Eladrin from their earlier incarnations (tieflings have been around a long time, and Eladrin used to be in Planescapes only
Warriors of Heaven in 2nd ed). Dragonborn are an entirely new race but nothing spectacular. They get a breath attack of an element you choose at character creation and can use it as an encounter power.
Armor Class, Will, Reflex and Fortitude are all now "Defenses" and no longer saves. Various attacks target the different defenses; saving throws have been made easier though. Roll a d20. Did you roll 10 or higher? You succeded! Did you roll 9 or lower? FAILURE.
I could go on and on for pages but its a lot of little things they changed. At the core, its still Dungeons and Dragons. Me myself and I happen to love 4th edition; and I
LOVE the direction they took
Forgotten Realms.