"In my opinion": I think people are being far too critical. I think the authorities made the right decision, bearing in mind they had to react very quickly.
Storming the place would have been disasterous, even the sharpest shooters in the world would have a hard time getting their targets quickly and accurately in a paniced mass of hundreds of people. The terrorists would have too much time then and could have started spraying bullets or grenades....how may would have died then?!
Also the use of a less potent gas would have the same drawback, the terrorists would have more time to react.
The SAS and the russian equivalents are highly trained professionals, but what did the ignorant think? That they could go in to a darkened room with hundreds of people, with all guns blazing and get all the "baddies", with no innocent casualties? I dont think so!