I've had a couple of Patagonia suits now (and tried a few more), and so can probably speak with some idea....
R2 (2mm UK summer suit) - Pretty flexible, but not as much as a 3/2 Flashbomb/Xcel. Seams leak from new due to the way it's stitched, but once you get over the initial leaking, it keeps you super warm (warmer than a normal 3/2 I think). I surfed in mine last year from mid April to mid December in Cornwall, with a thermal rashie in December, and wasn't really ever cold. Now in it's 2nd year, and looks like new.
R3 (3mm UK winter, with 2mm Hood) - Probably about as flexible as a top end 5/4 in my opinion. I've also got a Xcel infinti with is as flexi, but thicker. The seams on the hood leak as they suffer from the same stitching problem as the R2 (basically the neoprene is too thin to double stitch properly). Heavy when wet. BUT, I've surfed mine all winter in Cornwall, and not been cold. Again in it's 2nd year, and is pretty immaculate, aside from where I got the seams in the hood taped on the inside.
R4 (5mm, Norway etc) - Borrowed a mates one of these where the seams had all gone. Got in the water, and water came in through the seams, so was initially cold. After getting over the initial leaks, it was hands down the warmest suit I've ever surfed in. I was actually sweating in February, and letting water to cool down. BUT, it's heavy and not very flexible, and I felt a little like the Michelin Man.
I've found with all of the suits I've worn from Patagonia, that you need to keep moving. The more you move, the hotter you get, and I think in that way they retain way more heat than a normal wetsuit, but they are heavier when wet, and less stretchy. They're also so much easier to put on than a normal wetsuit (especially when wet), as you're putting your legs/torso/arms through wool, rather than rubber. And they feel snug (gay I know, but they do).
So, I like them, but I'm not sure they're as good as the hype. Personally, if you're going to spend £400 on a wetsuit I'd go for an Xcel Drylock or similar, but bear in mind it won't dry as quickly, nor will it have the Patagonia lifetime warranty. Overall, I think they last better than a normal wettie these days, but they're not perfect!
If you're interested, I might be selling my hooded R3 (size medium), as I've been given a new Xcel....