The module itself is very much a site-based dungeon-crawl. It's a good one, so if your group enjoys those kind of games, you should be well set.
The package also contains a pretty nice mini-setting, with enough info for the GM to run the game, but plenty of room for expansion. There's even a Player's Guide to help introduce your players to the area (it assumes that they are creating new characters, but it's easily adaptable). The inclusion of the mini-setting also gives lots of plot hooks to break up the dungeon-bashing if you wish.
With third level characters, you'll either need to increase the CRs for at least the first third of the module (and probably two-thirds or more) or find other ways to increase the difficulty for a better challenge. The module has some pretty tough encounters for characters of the modules expected level, but if you're two levels ahead of that it would probably be too easy as written. Leaving all the ELs as they are and slapping a tight timeframe on the first third might make for a fun challenge for 3rd level PCs, though.