My take is it's similar but different; better is hard to quantify. A well setup GTS2M corner cuts more effortlessly for me; that's sometimes a pro, sometimes a con if my accuracy is off. The GTS3M corner cuts just fine, mind you, and I have not spent any time trying to optimize the tensions, which are very configurable. I still haven't spent a lot of time trying to fine-tune it because it's just fine the way it is for me right now.
The GTS3's factory magnets are definitely stronger. I've preferred weaker magnets in the past but I actually like the stronger feel on this puzzle, especially for blind.
Stickerless shades are less "washed out" vs. the GTS2 and provide better contrast IMO. The plastic is thin enough that strong light can show through a little and look weird, but it isn't much worse than my other stickerless puzzles.
The ridges are very subtle but I love them and hope this is "a thing" for future flagship 3x3s. It's just enough grip reassurance, highly appreciated especially during blind.
It's ever-so-slightly larger than the current flagships, which might be a plus or minus for individual OH preferences (I'm a minute and a half OH solver sooooo... I hardly care lol)
It's as main-worthy as any of the other flagship stickerless 3x3s I've tried, which includes the GTS2M, Valk 3M, and HuangLong M. I like all of the above but the GTS3M has been getting the most use lately.