It depends really. As far as playing for fun, it's got a lot going for it. Randomized dungeons with rogue-like elements are endlessly repeatable, so it'll be perfect for players interested in just doing something different and fun for awhile. For the hardcore, it probably won't provide too much until they add the later levels, where it's supposedly going to be incredibly challenging. If it provides good to great exp, it'll pretty much always be relevant because it sounds like a really fun way to level alternate classes. I know I'd rather run through a cool, randomized dungeon experience to level than just spam the same dungeon or FATEs or Levequests.It will be especially helpful for leveling DPS classes, since queue times are so much higher.
Overall, I think it's more intended to be "fun" than "incredibly useful". There are plans to add more levels as patches go on as well, so the weapon may still stay relevant as long as its upgraded over time. I think Tome gear (since it takes longer to acquire and upgrade) might still be superior, but it'll likely serve as a great, fun way to get a decent weapon. I totally understand the concern though. It's only one week until it comes out though!