Results

 After spending a couple of nights playing just demos and trial games, here's what I found out. 

1) XBL Arcade games are really overpriced, especially all the old school arcade remakes.

2) Some demos are "multiplayer only" demos, but they aren't listed as such @ Arcade. So you end up playing with just one other person online, on a game designed for 16. (You see, I download all the old demos a hadn't played before, so some games were really old.)

3)Dead or Alive 4 is hard to master, especially if you've never played any of the DOD series (which I hadn't).

4)Some game trials only let you play for a limited time (ie. Tretris Splash... 5 minutes). Are they f**king kidding? No way you get the full experience of a game in just 5 minutes. Or card games that  deal you the same hand over and over again (ie. UNO Rush and Funtown Mahjong) until you buy the game. And don't get me started on Hasbro's Family Fame Night.

5) Found some cool/fun games. (See List Below)

Past Games:

Soul Calibur IV

Virtua Fighter 5

Ninja Gaiden II

UNO

1942: Joint Strike

Exit

Tetris Splash (I hate the demo, but not the game)

Zuma

Current Games:

F.E.A.R. 2

H.A.W.X.   (mediocre, but fun to play)

Resident Evil 5

Halo Wars

Peggle

Exit 2

Gin Rummy

The Dishwasher: Dead Samurai

The Maw

Future Releases:

Chronicles of Riddick: Dark Athena (movie sucked, but game seems cool)

I ended up buying: Peggle; UNO; Gin Rummy; Zuma; and, The Dishwasher: Dead Samurai. I'll buy the others at some other time, got plenty of games to play already.