Darkweavers are 9 HD medium-sized aberrations that take a shadowy, spider-squid-ish shape.
Their chassis is relatively poor. Aberration HD aren't the greatest, and while bonuses to all stats are nice they don't get exceptionally high in any given area. 20 ft. land speed is very slow, 20 ft. climb speed nearly irrelevant, as is DR 5/magic. SR 16 is the mixed bag it always was. Cold resistance 10 is a neat perk, and so is fast healing 3, so you got those at least.
In terms of natural attacks, the darkweaver... still sucks. Four 1d4 tentacles don't really cut it at ECL 9 (even if they have reach), and the 1d6 bite is only notable for letting you wield mouthpick weapons and damaging strength on a hit. Improved grab on the tentacles is worth something I guess.
Special qualities are better. Shadowstuff Armor is a free +4 deflection bonus to AC, and technically doesn't prevent you from wearing other gear (even though that might've been the intention). All-Around Vision isn't too notable, but occasionally great to have. Shadow Jump is pretty fun, and as long as Shadow Strands are up it can be used.
Shadow Strands, the darkweaver's signature trait, is interesting. It can be turned on and off at-will, and creates a 60 ft. radius aura of progressively worsening concealment (and anything more than 20 ft. away through the shadows gets total concealment). Darkvision and Blindsight can't get around it (though tremorsense presumably can), and on top of its concealment effects it also prevents creatures from easily moving away from the darkweaver. Whether that's a good thing is up for debate: +8 constitution and aberration HD result in less bulk than most monsters have, but it's an interesting niche at least. It also helps alleviate the effects of light sensitivity.
Finally, the SLAs. 3/day Confusion, Darkness, Suggestion, Tongues, and Web are all useful, but not world-shaking. 1/day Shadow Walk gives you something like the 9th-level wizard's Teleport combined with the 9th-level cleric's Plane Shift, but different in various ways. It'll add utility if you don't have both of those classes already, I suppose.
All things considered, I'm just not sure what a darkweaver PC is supposed to do. You can offer concealment to allies, but it'll restrict their movement. You can (kinda) lock enemies down, but you'll also guard them from ranged attacks. Your stats aren't actually that great for melee, and while the random chassis traits are useful they do feel a bit on the underwhelming side. Also, there's the whole thing where most magic items just don't work with your body shape.
I can see arguments for both +0 and -0 here. In the end, the sheer versatility and number of tricks this gets mean that something will be useful enough to warrant a LA of +0.