I wonder, if you are in the wrong forum, since this is the Runequest Forum. Are you intending to compare 4th Edition D&D to Runequest, which would probably result in a long thread, or do you want advice for running your 4th Edition game?
If it is the latter, you can get a lot of good advice on one of these forums: http://www.dragonavenue.com./ or http://okayyourturn.yuku.com/
You'll also find lots of arguments there over whether 4E is superior to 3E or the worst thing to happen to D&D in history. Here, you'll mainly find people claiming that any edition of D&D was a bad idea and 4th Edition does not make anything better.
If the former, then I'd have to say that 4th Edition D&D is a lot different from Runequest. Everything that the anti-D&D people here hate about 3rd Edition has been amplified in 4th Edition, and everything that the 4th Edition fans this is an improvement over 3rd is the opposite of how things are in Runequest.
Myself, I am a fan of both 3rd Edition and Runequest. I can see what they were trying to do in 4th Edition, but I think they botched their Game Design role. It looks good because it is new and shiney, but it is so inherently flawed that I don't think I would ever try to run a game in that system. My next game is going to be 3rd Edition, but one day, in MY life time, I plan to run a Runequest game.
Many of the 4th Edition fans are raving about how easy it is to create a character, especially compared to 3rd Edition. Reading the forums above, I think that if they dislike 3rd Edition that much, they'd probably HATE Runequest.
The difference is that in Runequest, you have no guidance in how to make your character; all you have is a bunch of skills and you have to decide how much to put in each skill. There are no classes to tell you what to do, and you have to decide your own destiny. It is really easy in Runequest to make a character who either so specialized he doesn't have much chance of surviving in the field, or else is so spread out that she can't really be effective at anything.
(On the other hand, since in Runequest, about the only thing you have is a list of skills, that makes things a little simpler than D&D were there are skills and feats and powers and classes.)
In 4th Edition, moreso than 3rd, you have classes to guide you as to what to do. This is both the number one reason for loving 4th Edition and the number one reason for hating it. To summarize much discussion on the other boards:
4th Edition is AWESOME! You just pick a class, and it gives you your list of powers, the skills you can take, and what tactics you can use. Every character has a decent chance in both combat and skill challenges No more feeling inadequate because my Dervish can't get through the Iron Golem's DR or my Wizard is out of spells.
I'm sure that the time it takes to make a character will go down once you get used to a game. At www.dragonavenue.com, they are talking about cards they've made which have the powers written on them, so instead of flipping through the book, the player can just look through the cards and pick out what he wants. (The cards are designed to be used in the game, but I can see that they'd be very handy in character creation, too.) The 4E fans say it is much easier to make high level characters, which should be helpful for the DM.
4th Edition SUCKS! Everything is dictated by your character class. Multiclassing has been gimped. You can now only take two classes at most, and you practically need a lawyer to do that! And each class is so much more rigid and flexible than before! You can't make a decent archer unless you're a Ranger, and if you are a Ranger, then you either HAVE to rely on bow and arrow, or else use two weapons. There is no flexibility. I am sticking with 3rd Edition.
And there you have it. If you love Runequest, you'll probably hate 4th Edition D&D. If you love 4th Edition D&D, you'll probably hate Runequest. I predict a lot of 3rd Edition players will probably switch to Runequest.
(I tried to get the guy at my local store to stock Runequest stuff, but I couldn't promise I'd buy the books because I actually have what I need already. I don't know what can be done to get the books into the stores, but I think if they get stocked, they'll probably sell.)