I played the GU games when they first came out, and I went through the HD collection a couple years ago. I personally don't think they hold up very well, but I do think they're better than the original .hack games that you really liked (which I dropped mid-way through Volume 3), so you may still enjoy GU regardless. There's still a lot of time-wasting menu navigation that really hurts the pacing, and the general story structure of the three games is highly repetitive. Combat is fun (this is the biggest improvement over the original series imo), but it lacks depth, especially by the standards of more recent action JRPGs.
It's also worth noting that the fourth volume included with the HD collection is not a full game, but a 2-3 hour playable epilogue.