Earlier this 
week, we were looking for co-op type of games for the XBOX: we weren’t looking for the typical ‘splitscreen’ first person shooter, so Halo and that kind was out. Eventually we settled on ‘Mortal Kombat: Shaolin Monks’, which allows 2 players to work their way through all the levels. This ended up to be quite fun but at times, say uh, tedious and repetitive. I noticed that there aren’t too many co-op games out there: a good reference I found in this About.com posting, ‘Top Ten Best Co-Op Games on XBOX’.
This also reminds me of the question asked at the local EB Games: where are the typical Shoot-em-ups arcade games for the XBOX. I mean, games in the style of Salamander, Nemesis (Gradius as many other people may know this game for) and R-Type. Glancing through a short-list of games (all of them tagged as ‘shoot-em-up’) seems to suggest that nowadays a ‘shoot-em-up’ game equates to a first-person shooter game. I guess, semantically that would be correct.
Update: More on ‘Shoot’em ups’ at Wikipedia.