Well, I played 4e quite a lot by now. Most time as Dungeon Master, but also some sessions as PC.
In my opinion the 4th edition is great (not perfect, but an improvement compared to 3.5). I think, there are several people who dislike the 4th edition. Probably the best would be to try the 4e yourself. Everyone has different demands concerning roleplaying games: Some like more the roleplaying parts, others like more the kick-in-the-door style of gaming and want to slay hords of monsters.
Nevertheless, in this post I want to try to state why I like the 4th edition.
One of the biggest changes has been the simplification of the rules, but without making them to simple. Nearly everything which should be covered in the rules seems to be covered to me. The advantages of simplier rules are (IMO):
- New players can faster get to play and do not have to read that much stuff.
- You can memorize the rules easier. That means less time is wasted by looking stuff up.
- Not so many rules in the rulebooks you need once in a year, which prevent you from finding what you are really looking for.
Some were complaining that the rules are too much focused on combat. Anyhow, I think, you just need more rules for combat to balance the game, while needing far less rules for roleplaying.
Another step forward is the power system. This makes classes like the fighter far more interesting, because you do not do the same standard attack each round. Each character class has mostly every round in combat the choice between different powers.
The power system is one enhancement to the fights, but not the only one. Moreover, the terrain, placement and movement has become far more important. There are many situation where you get an advantage if you move (or move your enemy with a power) to the right spot instead of standing the whole fight at the same square.
Another good point is, that you generally won't fight one single enemy, but multiple enemies at one time. This also makes the combat more exciting. Nevertheless, you can get thrilling boss fight against so callad solo monsters (like – of course – Dragons).
For me as Dungeon Master I can also say, it is much more fun to prepare the session in the 4th edition. With 3.5e I had always to think twice if a encounter is really balanced and after all I had to see during play that it wasn't. But the XP buy system in the 4th edition works out very well and is very easy to use.
After all, I want to say some words to the rulebooks: These are much better structured than in 3.5e. You find the rules you are looking for much more easier and the monster stat blocks are much better to read. Also I like the concept art in the core rulebooks (not all new rulebooks).
In spite of all these positive points I have to state one negative point: The selection of Magic Items in the Player's Handbook is far to small and those items are mostly boring. Therefore you should also buy the Adventurer's Fault, which contains tons of magic items.
I hope this article helps. Probably I could say much more, but this should be the most important and is what came spontaneously to my mind. I recommend to search for other opinions in the web, if you are undecided if you like the 4th edition, or even better, as said before, to play it yourself, if you have the possibility (maybe in a local game store).