IMO REGN looks like a high quality research outfit (lots of papers in high quality journals). As an example, here is a link a recent paper in Nature (Note: that Genentech has similar research in the same issue).
However, the CNTF failure made me question REGN. They found a high percentage of neutralizing antibodies to CNTF in a phase III trial (pleasse correct me if I am wrong). It would seem to me that when you are running a trial on a recombinant protein one of the first things that you want to look for are neutralizing antibodies. I just don't see how they could have missed this in the Phase I and II trials.
Neutralizing antibodies could be an issue with their VEGF trap, a non-native fusion protein.
I don't short stocks, but the current price seems expensive to me. If it were to fall below $10, I would consider a purchase of REGN.