So i got an XBOX and LIVE - now what games should i get?

[QuickStop]

so far ive got

rallisport challenge 2 - really good
ESPN NHL 2K5 - really good
Top Spin - really good
Mech Assault - meh offline, really good with 2 people online
Crimson Skies - really good
Splinter Cell Pandora Tomorrow (borrowing from friend) - good but i havent gotten the hang of it yet
Halo(borrowing from friend) - XBconnect - good, but im a noob compared to the people that play cause ive only played it for probably 5 hours or so ever