Metal Gear Solid 4 was by far the biggest third-party title exclusive on the PS3 this year. It's the end of the line for the Solid Snake tetralogy, and it's a milestone that every hardcore Metal Gear fans should already have in their collection. However, more cash-savvy fans know Kojima Productions likes to re-release MGS games, possibly leaving some to wait out the usual extra year or so for a souped up version.
If you find yourself in the latter category and haven't tried the game out yet but want to, the demo that's available on the Japanese PS Store should give a taste of Snake's last adventure. The 1.4GB download can only be grabbed off the Japanese PS Store (so far, since the other regions have not updated yet); so make sure you've got an appropriate account.
[Thanks Amish G. and Mike!]