I have, and I have very little love for GU compared to IMOQ. In my opinion, the inferior .hack was remastered, as GU fails to live up to its predecessor in nearly every department. For starters, the characters and story are absolutely nonsensical and play out like a confusing fanfiction based on the stories that came before it. Without going too far into spoilers, basically there was this group of big bads in IMOQ called Phases that were supposedly unstoppable, rogue programs hellbent on destruction. In GU, certain playable characters are aligned with these Phases, allowing them to summon Avatars of them. Of course, Haseo, our resident edgelord, is aligned with Skeith, the first (and coolest) phase also known as The Terror of Death. It's so edge, you'll find cuts mysteriously appearing on your body as you play. The overall writing is just so heavy-handed that it seems to forget sometimes that this is an MMO and the characters we're playing as are being "controlled" by real people on PCs. I mean yes, the characters talk about the real world and there's plenty of real-world elements like news stories and forums, but what happens inside The World gets so over the top, it really just leaves the realm of possibility for what could happen to a corrupt AI/video game.
The gameplay is basically a dungeon crawling hack and slash (think Phantasy Star Online, the game .hack was heavily inspired by), but it streamlines IMOQ's very menu-heavy gameplay, which admittedly does make the combat snappier. Also, Kite in IMOQ only has access to one weapon, while Haseo starts with only one but eventually gains access to three others, giving you more variety. Now, a lot of people prefer GU's combat since you're not pausing it constantly to go through seven menus to use an item or order a party member to heal. I prefer the original style, but this aspect is more subjective. I thought the combat was fine, but very repetitive.
The exploration in GU is a lot more boring, due to the lack of variety in the fields and dungeons. IMOQ had 8 different fields and 4 different dungeons across all 4 entries. In GU, you'll often find yourself in the same 1 or 2 fields and dungeons until the third entry, which introduces 1 or 2 more but then abandons the previous ones. In other words, the areas are horrifically repetitive and you'll get sick of them real fast. It doesn't help that the music is far from as memorable as IMOQ's OST, so being in the same areas constantly also means you'll be hearing the same uninspired tracks over and over.
I'd give the original IMOQ series a 9/10 with nostalgia glasses on and an 8/10 with them off. As for GU, I'd go 5/10 with my hate hat on and a 6/10 with it off. It's not a bad game, but it's just not as interesting as IMOQ. Back when GU came out, I saw people saying it was darker and more mature because it had cursing, which should tell you all you need to know about the story. But, it's not a bad time waster and does do some interesting things like Avatar battles, Haseo's class variations, and the Arena. Just don't expect anything groundbreaking.
Of course, all of my complaints are moot since GU's pure fanservice sold better than IMOQ, so that's why it's the one that got the remaster (plus it didn't look as bad as IMOQ does, so it was probably easier to clean up). Sigh.