Basic/Expert/Master/et al. was a loose system, gamers were expected to fill in the gaps with their own house rules. There were 7 options for players- (Human) Fighter, (Human) Cleric, (Human) Thief, (Human) Magic User, Elf (Fighter/Magic User), Dwarf, & Halfling. So the generic classes were all human and the 3 other races were their own class. Other options became available later on.
Advanced D&D, First Edition, was written with the idea of standardizing rules for tournament play. So that everyone playing AD&D used the same rules and knew what to expect at tournament conventions.
AD&D had a broader range of options than Basic. Races available to PC's were Dwarf, Elf, Gnome, Halfling, Half Elf, Half Orc, & Human. Available classes were Cleric, Druid, Fighter, Paladin, Ranger, Magic User, Illusioinist, Thief, Assassin, Monk, & Bard. Humans could be any one class. Non-humans could have more than one class at the same time, but some classes were off limits to them.
First Edition AD&D mechanics were driven by game balance. Each character had a few skills he was good at. But he couldn't do it all. So you had to get help from friends and have them play characters who were good at other things. The more a character could do- the more experience points it took for that character to level up.
Full Disclosure: I prefer 1e AD&D to other rules.
Second Edition AD&D took all the naughty stuff out, such as Assassins, Half Orcs, Demons & Devils. It crippled Bards to make them more 'fair'. Monks dissappeared. Gary Gygax's name was chiseled off all monuments and royalty checks in Lake Geneva.
To replace all that, 2e gave us 8 flavors of Magic User, called school specialists. And primitive rifles. Oh and kits. 2e introduced kits for people who couldn't figure out how to give their characters flavor or personality on their own.
WoTC bought the game from bankrupt TSR. WoTC wanted to sell new books & knew they couldn't sell fans recycled AD&D rules, the fans already had them. So they sold a paper version of Diablo. When that actually worked, they put out D&D 3.5 to see how many would fall for that.
3e lets players be any race they want, and any class they want. When its time to level up, you can pick a different class and add a level of that class to your pc. And a PC can learn any skill or feat they want. So none of the classes are special or unique, cause they all have varying amounts of access to the same talent pool.
Honestly I've only glanced at 4th edition D&D. Dragonkin...has it come to this? Fire breathing lizardmen? Where is the challenge if you play something this powerful? And they thought 1e Bards were bad.
I also can't figure out the reason to have Eladrin when they are just the same as elves. Maybe they taste different to monsters. It seems like filler or a waste of space to put in elves... then something that is just like elves but we'll call it something else.
What do I suggest? Buy previous editions. They're cheaper than the new books and you won't feel like a sucker when they come out with version 4.5 next year. Better yet google OSRIC. Because those rules are completely FREE.