Hi Miranda,
I haven't tried Look road pedals but I have Ultegra pedals and my bf has Dura Ace pedals. We tend to switch bikes for a ride or two when we change things up to get the other persons take on it (we're almost exactly the same size), so I've ridden his pedals a fair amount. Besides the weight, I would say the Dura Ace pedals have better bearings -- they spin much easier. I notice this when I spin the pedal with my hand; of course, I'm not actually aware of it when I pedal.
There are two comments I would make about these pedals.
1. The pedals "loosen up" with use. They really do -- my bf got his pedals after I'd had mine a year or two and was quite used to clipping out with them. I noticed his new Dura Ace pedals were considerably "crisper" than my pedals (though I didn't have trouble clipping out of them). Over time, his pedals have gotten easier.
2. You get used to the force they take. When I first got my Ultegra pedals
(which were my first experience with clipless pedals), I thought there was something wrong with my cleats or pedals or something

. I just couldn't get out. Of course, there was nothing wrong with the pedals, it was a head thing and a kinetic memory thing. After a few months they were magically MUCH easier

.
Also, I don't have to look down to clip in (although I'm sure I do sometimes

). But they hang in an easily-accessible position.
I *love* how solid these pedals are. After having eggbeaters on my commute bike for two years, I'm switching to a different pedal that I hope will be more like my road pedals -- I much prefer that solid, locked-in feeling to the floaty feeling my eggbeaters have.
Good luck with whichever pedals you get!