After a quick read, ISTM that Dagger will be subject to serious attacks from ASICS. The basic issue is that (if I'm reading the spec right), the lowest level DAG values are only computed once per block, as opposed to once per nonce. That means that mining doesn't require 512MB/thread at all; it requires 512MB of precomputed data with lots of read ports. This means that it would be subject to attack on a (rather large) ASIC that is willing to include such a beast. (Alternatively, a TMTO algorithm could read the 512MB sequentially, appending to various hash pieces as it goes.)
I don't see why a difficult-to-compute, easy-to-verify hash is any better than a symmetric hash where you have to start over for each nonce.
(As a more trivial issue, the Dagger wiki page seems to be confused as to how many lowest-level nodes are hashed together: the text says 8, but the pseudocode says 4.)