Great hacking game, with lots of missions and upgrades
There's a great load of upgrades you can buy, including new software, better gateways and security systems. These can enable you to crack passwords faster, store more data, or bypass security systems on other computers.
There is a storyline, but from what I've done of it it seems to be optional. There are unlimited missions you can do, starting from simply deleting or copying files, to hacking banks and tracing balance transfers, or changing someones academic details.
Only bad thing I've noticed is the IRC that you can buy in the game. The community seems to be fan-run, though the admins are pricks, and will happily ban you for nothing.
Overall, it's a great game, and I'd recommend it to anyone who wants a change from strategy games.