Along with Arch Enemy, probably the best melodic death bands ever to grace the planet.
Also, they are the one of the few bands that remain constantly awesome throughtout their whole career and don't water down their music to attract a larger audience.
They have the most harmonious riffs ever, with nice groovy drumtracks and a spectacular keyboard player. In fact, they are so harmonious and melodic, you swear they have an invisble conductor while they perform live.
Dark Tranquillity is also a really good live band, as they care about their fans and the singer jumps in the crowd all the time.
However, the singer is a tad strange, as he does these really weird motions when he performs live. That doesn't change the fact they kick ass on a biblical scale.
When something is so horrible, so fucking bad quality, such a piece of shit that it's appealing as going to a festival to view and discuss various fecal matters that parted ways with different animal anus holes.