Just from the Corebook I like the looks of playing a fortune driven Void-Master or Explorator (because Tech-Priests and the Adeptus Mechanicus ftw!). That or a prideful Navigator.

I have access to supplements, though I think for myself I'd limit my own options to the corebook so I can ease myself into the game, bit by bit. I do have experience playing in games of Deathwatch and other 40k rpgs though.
I'm old hat when it comes to the setting though. I used to grab White Dwarf in the mid-90s, owned the Space Crusade boardgame, Necromunda, Blood Bowl (played this a shit-ton! My Skaven never lost a match!), Battlefleet Gothic... Just so happened to be a Geedubs start in my city around '95-96 and I liked the models.
I'm much more a tabletop player than a lore dude, though I admire both and now I own the RT rpg, I figured I'd add myself to the pot here. :)