Paper:
Delusional bias is a fundamental source of error in approximate Q-learning. To date, the only techniques that explicitly address delusion require comprehensive search using tabular value estimates. In this paper, we develop efficient methods to mitigate delusional bias by training Q-approximators with labels that are "consistent" with the underlying greedy policy class. We introduce a simple penalization scheme that encourages Q-labels used across training batches to remain (jointly) consistent with the expressible policy class. We also propose a search framework that allows multiple Q-approximators to be generated and tracked, thus mitigating the effect of premature (implicit) policy commitments. Experimental results demonstrate that these methods can improve the performance of Q-learning in a variety of Atari games, sometimes dramatically.

Review:
A recent paper by Lu et al introduced delusional bias in Q-learning, an error due to the max in the Bellman backup not being consistent with the policy representation implied by the greedy operator applied to the approximated value function. That work proposed a consistent algorithm for small and finite state spaces, which essentially enumerates over realizable policies. This paper proposes an algorithm for overcoming delusional bias in large state spaces. The idea is to add to the Q-learning objective a smooth penalty term that induces approximate consistency, and search over possible Q-function approximators. Several heuristic methods are proposed for this search, and results are demonstrated in Atari domains.
I found the topic of the paper very interesting - delusional bias is an intriguing aspect of Q learning, and the approach of Lu et al is severely limited to discrete and small state spaces. Thus, tackling the large state space problem is worthy and definitely not trivial. 
The authors’ proposed solution of combining a smooth penalty for approximate consistency and search over regressors makes sense. The implementation of the search (Sec 3.4) is not trivial, and builds on a number of heuristics, but given the difficulty of the problem, I expect that the first proposed solution will not be straightforward.
I am, however, concerned with the evaluation of the method and its practicality, as reflected by the following issues: 
1. The method has many hyper parameters. The most salient one, \lambda, the penalty coefficient, is changed between 0.25 to 2 on the consistency penalty experiment, and between 1 to 1000 in the full ConQUR experiments. I did not understand the order of magnitude change between the experiments, and more importantly, how can one know a reasonable \lambda, and an annealing schedule for it in advance. 
2. I do not understand the statistical significance of the results. For example, with the constant \lambda=0.5, the authors report beating the baseline in 11 out of 19 games. That’s probably not statistically significant enough to claim improvement. Also, only one run is performed for each game; adding more runs might make the results clearer. 
3. The claim that with the best \lambda for each game, the method outperforms the baseline in 16 out 19 games seems more significant, but testing an optimal hyper parameter for each game is not fair. Statistically speaking, *even if the parameter \lambda was set to a constant zero* for the 5 runs that the method is tested on, and the best performing run was taken for evaluation against the baseline, that would have given a strong advantage to the proposed method over the baseline….
4. For the full ConQUR, there are many more hyper parameters, which I did not understand the intuition how to choose. Again, I do not understand how the results establish any statistically significant claim. For example, what does: “CONQUR wins by at least a 10% margin in 20 games, while 22 games see improvements of 1–10% and 8 games show little effect (plus/minus 1%) and 7 games show a decline of greater than 1% (most are 1–6% with the exception of Centipede at -12% and IceHockey at -86%)” mean? How can I understand from this that ConQUR is really better? Establishing a clearer evaluation metric, and using well-accepted statistical tests would greatly help the paper. At the minimum, add error bars to the figures!
5. While evaluating on Atari shows applicability to large state spaces, it is hard to understand from it whether the (claimed) advantage of the method is due to the delusional bias effect, or some other factor (like implicit regularization due to the penalty term in the loss). In addition, it is hard to understand the different approximations in the method. For example, how does the proposed consistency penalty approximate the true consistency? These could all be evaluated on the simple MDP example of Lu et al. I strongly advise the authors to add such an evaluation, which is easy to implement, and will show exactly how the approximations in the approach deal with delusional bias. It will also be easier to demonstrate the effects of the different hyper parameters in a toy domain.