I was excited when this place first opened in my neighborhood (South Loop) because there aren't many trendy nightlife options around there, and I was a bit dissapointed when Tantrum wasn't the crazy nightlife scene I had envisioned it to be. However, I came to like how the place ended up being. It's a small cozy little place to grab a drink before you're headed somewhere or after you've come from someplace. Definitely don't expect this place to be a seen-and-be-seen spot- I guess that was never their intention.
Basically, Tantrum still retains a hip atmosphere without trying too hard. It's actually a nice, chill alternative to the sweaty, over-crowded bump n'grind lounges and clubs that most places turn out to be. I'm not a huge martini fan, but I tried a couple and they're pretty good.
Pros: Lounge-like, laidback atmosphere
Cons: Not a lot of people