tl;dr the first half and second half ruin each other
Unfortunately, Durarara falls far short of Baccano's mark (as anime). While it does have its fair of engaging characters, such as Celty, Anri, Shizuo, and Izaya, most are a sore disappointment knowing what the mastermind was capable of.
That namely centers on the cliche trio that spent the entire first half of the anime being, ostensibly, the only sane people observing the insane Ikebukuro. And for what it's worth, I found myself enjoying the show in anticipation right until I was letdown by their actual fruition, which would be about the first 10-13 episodes.
And honestly, with little to no foreshadowing beforehand in the anime, the first half of the episodes and the second half simply clash too much due to the poor transition between them.
I won't go into further depth because, as the case were, the first half was largely unique to the anime (i.e. not in the light novel Durarara was adapted from).
I'll watch season 2 with no expectations.