Flaber, I dont think this is flat and boring at all. In the end design is just visual communication not art, and for a poster i think this just works.
I have to say that I can undertand all the common mistakes you did because I started the very same way you just did with this poster. First of all, all those workarounds to get that "fashion-y" look on this poster without knowing -how to do it- really amazed me.. I wish i could have done that the first time I designed a poster for someone else, seriouslly.
Ok so, text: You have spacing problems and i could write a huge post about it but gomediazine made it easier for both of us:
http://www.gomediazine.com/design-tip/rule-four-spacing-is-your-friend/
Try to balance everything, titles on top, details on bottom, align everything correctly, if a logo its important make it bigger, if its not make it smaller; Think about it, what should I read first? Price? Date? etc. After that is just a matter of spacing everything correctly.
DPI: http://en.wikipedia.org/wiki/Dots_per_inch
Colors, as you work on projects like this you will understand how printed stuff works. (CMYK process etc) Basically, i would change those neon-y colors for something more red-ish or something a bit different because if it gets printed its going to look really, really saturated against that dark background.
Hmm, check out gomediazine they have some really nice articles about everything im trying to explain. I suppose you used Photoshop for this?
(Ps. damn sorry for my english but im freaking busy right now)