I equate Robin with Rachel, in that they're the "hot" girl characters which allows them to conceal the fact that there's little of substance underneath their exteriors.
Apart from the whole "Canadian tomboy" thing, which mostly manifests itself externally, I don't find a lot to like personally about Robin. Lily has her moments but she is more captivating, and most of the time endearing.
I haven't seen beyond the beginning of Season 5, so my opinions of Barney and Robin are likely subject to change.
I love Jason Segel.
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SuperNiceDog shoots the lights out