If you haven't seen the first series, make sure you buy it before watching season 2. Many references are made to the previous season and I get the impression it would be hard to keep up if you're not familiar with the characters and their backgrounds.
All the characters you know and love are back and just as witty as before. There are some new characters which are intriguing and my personal favourite, Dick Casablancas and his brother Beaver become series regulars, with Dick providing a huge chunk of the humour. As mentioned before, the set up is slightly different with one season long mystery (the bus crash), a several episodes long mystery arc (the fall out from the fight on the bridge we saw in the season 1 finale), a couple of smaller arcs and the obligatory `mystery of the week'
There are some nice extras to make up for the lack of them on the previous box set. A day on the set with Veronica Mars shows that Kristen Bell is every bit as charismatic as Veronica. A gag real and deleted scenes are also a nice edition.
This season is slightly under the par set by season one, but no less enjoyable. Due to the many mystery arcs, it can get a little hard to follow sometimes but stick with it, you'll be rewarded! The season finale is awesome and seems to wrap up the two seasons nicely in anticipation for the upcoming third.
Don't be put off by the `teen drama' tag, My Mum is in her fifties and she has finished season one and is onto season two and loves it.
Basically, if you liked season 1, buy season 2. I'm pretty sure you won't regret it.