Yeah, I'm rather irritated every time they bring out a new edition, because the hundreds of dollars I've spent on the previous edition make me want to not spend another cent on the new books. :/
That being said, I really REALLY like 4th edition Dungeons and Dragons. Somewhere between 2nd edition and 3.5, there was this clutter of rules that didn't make any sense. People just made builds using the biggest and baddest (most recent) books, which made the older books even more outdated. Tome of Battle: Book of the Nine Swords? That thing almost wrecked our group- everyone wanted to play a swordsage or warblade or crusader, because they were so bad-assed that no one needed to play a fighter in the group. We had three of those, and no thieves in the group, and one mage. It was the most horribly unbalanced group I've ever played in.
In 4th edition, the power balance has been restored between classes. Everyone has something cool to do every round- whether you're a fighter or a wizard, you have powers to use each encounter, and powers to use every day. The daily powers are more powerful, and fun to use, and it's exciting to get to use them in combat.
Wizards are no longer 'tapped out' when they use a certain amount of spells- they're able to use basic cantrips, minor attack spells (like Magic Missile), and rituals whenever they want, although rituals (non-combat oriented spells) are only for use outside encounters.
Priests are no longer a portable box of band-aids, because every hero has a function called 'healing surges,' which allow them to restore a measure of their lost hit points. Clerics are still powerful, and they heal companions, but a new class (Warlord) also heals the heroes, so there's less emphasis on the cleric as a healbot. Heroes are also able to heal themselves once an encounter using a power called "Second Wind," so even without a healer, a party can function.
I like 4th edition, and I play it all the time. I DM games at the local game shop, teaching 4th edition to people (it's free to people playing in my games), and I like it.
If you're even curious, I would recommend finding a local game store, and seeing if you can sit in an a game. It's fun, and it should be pretty free.
-kv