I'm not an experienced puzzler yet, so take my opinion for what is worth. I.e. nearly nothing. But I have a positive opinion of the SW/SG puzzles. It was the Isis, actually, that sucked me into the whole puzzling vortex - including the Revomaze.
Overall I thought the Isis was pretty fun. I think it could be made into more of a "pure" puzzle by eliminating the clues and modifying the starting mechanism such that it was more easily discoverable through trial and/or reasoning.
Just opened the key chamber on the "G2" Ramisis last night. Was slightly disappointed by this one in that it didn't take all that much manipulation, listening, and fiddling to get things done. Once again, eliminating the clues (which I had decrypted on my own as with the Isis) might turn it into more of a pure puzzle. Haven't disassembled this one yet.
My Copernisis is "in the shop" right now. As noted by others, there have been some issues with planet pins coming loose. I'm sure they were held in their slots with some sort of adhesive that loosens due to the repeated lateral force that comes with precisely trying to count the number of position "clicks". SG has been very responsive regarding this issue and is replacing my puzzle with a new, slightly reengineered, version that uses threaded pins. Haven't quite solved this one yet, but I think I was about 99% done when my pins started to come out of the slots.
With some probing of the Kuku using a thin piece of paper, I think I know how this one works. I have, unfortunately, not gotten any movement in the pieces yet. Reading others comments, I'm wondering if I maybe have the "stuck together" issue described by others. I'll keep working on this one as time permits.
Then there is "The Sentinel". I have one of these, but haven't done much more than pick it up yet. Saving it for a suitable lull. My understanding is that this one isn't that difficult.
Finally, the iBall3. Not a puzzle exactly. But sorta. I actually really like this one, having "solved" the regular version and been upgraded to the red "elite" variant. Off all my puzzles, this is the one that I can pick up at any time and challenge my logical reasoning and memory skills.
My favorite so far, though, has been the Copernisis. Sorry bluesign2k.

I totally get people's concerns about needing the web site to solve the puzzle, the pins falling out, etc. But I still thought the overall "story" of this puzzle was quite entertaining. The progression from opening the secret chamber, solving the "equation" etched inside, applying the equation, the tie in to Copernicus, etc. A great story if you don't try to jump to the end quickly.
On the Revomaze side, I've solved only the Blue. Skipped the Green at Revomaster's suggestion and am working on a Bronze that he provided while I'm waiting for my (pre-assembled) CE. Also have an outstanding order for an Orange.
Overall I find the Revomaze (thus far) more "technical" in nature with a bit less pageantry than the Isis series. And I'm sure that is what many of you like about the Revomaze compared to the Isis series. Personally, I don't mind the over-the-top drama of the SG puzzles. A little drama is fun sometimes. I have both Revomazes and my Isis puzzles on my desk and people tend to gravitate towards the Isis first. I'm certainly not saying it is a better puzzle than a Revomaze - just that it attracts people's attention more readily. And sucking people into puzzling is a good thing IMO.