IMO, there's something enjoyable about all the versions of YGO if one only lets oneself enjoy them, including Zexal. I've found the majority of the original fanbase is hardly willing to branch out and give any of the spinoffs a chance -- and by that I don't mean simply watching them, but opening their minds to them and not deciding before even really starting that it sucks and they hate it.
DM is nice, yes, though I am probably in the vast minority in thinking that while it was memorable and nostalgic, it's currently my least favorite of them in terms of how much I like it now, if only because I had a hard time really caring about most of the characters on a rewatch. The only one who really made me genuinely like him was Yuugi.
GX is... well, it's very hit or miss in every area, but it's probably my favorite as far as characters go. I really enjoyed seasons three and four, even though they were a dealbreaker for some people. But I loved Juudai's character development, and I only wish GX itself wasn't cursed with the lack of interest that develops by the end of any given related production, causing both the anime and manga to get cut short and rushed to completion because nobody cares anymore and wants to move onto the next shiny thing.
5D's is a very enthralling story up to the end of the Dark Signer arc, after which it gets a little shaky and arguably less enjoyable. Most people knock it for a single ridiculous concept they can't seem to let go of (OH GOD THEY CHANGED IT NOW IT SUCKS), but they fail to take into account everything else that's fun about it -- I didn't love everyone in 5D's as much as I did in GX, but I did discover some really beloved characters, and at least for the first half of the series, I liked the plot as well and thought it was a definite step up from GX.
Zexal so far is turning off a lot of the older fans for various reasons, but if the latest episode is any indication, it's just getting into serious plot now, so I'm sticking with it for now and waiting to see what direction it goes in. Yuuma is an endearing protagonist, and I'm looking forward to seeing how the whole Tsukumo parents thing unfolds at this point. Oddly, I appear to be the only one who really, really likes Cathy. :| Also, Astral is a boss.
I would highly recommend that people who naysay the spinoffs without trying them first watch at least one full season of them before passing them off as crap. Not just an episode or two, because it's impossible to get the full sense of any long-running anime from just a handful of episodes. And while we're at it, let's throw in not to judge the anime with DM-bias just because it doesn't have X number of characters from DM in a major role. They're all different, too, so it's not like if you hated GX you're going to hate 5D's, or vice versa. And if you manage to plow through a season of any of the spinoffs and wind up disliking it even then, well... congratulations, you now have an informed opinion!