It doesn't feel "open" like say Sun Devil Stadium, but the game experience is radically different, and better. I hate it when the roof is closed, I honestly avoid games when I know the roof will be closed, its so heavy and ominous feeling, I don't like it.
Since Chase Field was the first stadium in the world with a retractable roof and natural grass, it was something of a guinea pig.
I've never been to Seattle, but it seems to me that Safeco field has a much better design in this regard. It was built after Chase though, so it could learn from its mistakes. The tricky thing w/ Chase is, its roof is to keep heat out, whereas other stadiums are to keep rain out. So where Safeco can have a closed roof and an open outfield walls open (which keeps most of the moisture out), Chase has to be much more air tight for climate control.
As you can see in the first picture, Safecos roof slides off all to one side (which probably wasn't possible for Chase considering its tight footprint):
You must be registered for see images
Here from the inside, you can see the roof is closed, but the sides of the stadium remain open to provide views:
You must be registered for see images attach
Chase Field however has the roof split in two halves. Even when its completely open, there are many seats that still have portions of the roof over them. I suspect that if you're sitting in these sections, it feels very much like you're still in a dome. You can spot a few of the sections (along the top behind home plate, and along the top towards the end of the baselines):
You must be registered for see images
Luckily, the architects put a white opaque material on the arched trusses along either side of Chase Fields roof, which alllows light in, which is nice. You can see a bit of that below. I wish they would've used that (or windows, which would be even better) for the areas where the large Pepsi advertisements (which are now replaced w/ D'backs logos) are, it would add more visibility of the city, and allow for more shafts of light to enter the stadium:
You must be registered for see images
But ,you've hit on two subjects (sports and architecture) that I tend to ramble about far too much, so sorry this reply was so long.
The short answer: Roof closed & Panels closed<Roof Closed and panels open<Roof Open and Panels closed<Roof Open and Panels Open<Being in an outdoor stadium on a nice day