Undertow on XBLA

Has Bioshock given you a taste of high pressure depths?
Want to kill a few more Big Daddies but don't know how?
Well, Undertow might be the cure. With a plot that plays out like Jules Verne crossed with Jerry Bruckheimer, this is non stop action. The gameplay is fast, frenetic and (to begin with at least) pretty tough.
It reminded me of playing Guardian on the C64 - constantly having to get across the map to assault/defend spawn points.
Chair have done a great job with this XBLA title, and they have made the most of the limited memory/space to make an addictive High Def shooter that you'll keep coming back over and over again.
In my opinion this is the first must have title on the Arcade service.